[PATCH for-next V6 0/5] HW Device hot-removal support

[PATCH for-next V6 0/5] HW Device hot-removal support

[Yishai Hadas]

Currently, if there is any user space application using an IB device,
it is impossible to unload the HW device driver for this device.

Similarly, if the device is hot-unplugged or reset, the device driver
hardware removal flow blocks until all user contexts are destroyed.

This patchset removes the above limitations from both uverbs and ucma.

The IB-core and uverbs layers are still required to remain loaded as
long as there are user applications using the verbs API. However, the
hardware device drivers are not blocked any more by the user space
activity.

To support this, the hardware device needs to expose a new kernel API
named 'disassociate_ucontext'. The device driver is given a ucontext
to detach from, and it should block this user context from any future
hardware access. In the IB-core level, we use this interface to
deactivate all ucontext that address a specific device when handling a
remove_one callback for it.

In the RDMA-CM layer, a similar change is needed in the ucma module,
to prevent blocking of the remove_one operation. This allows for
hot-removal of devices with RDMA-CM users in the user space.

The first two patches are preparation for this series.
The first patch fixes a reference counting issue pointed by Jason Gunthorpe.
The second patch is a preparation step for deploying RCU for the device
removal flow.

The third patch introduces the new API between the HW device driver and
the IB core. For devices which implement the functionality, IB core
will use it in remove_one, disassociating any active ucontext from the
hardware device. Other drivers that didn't implement it will behave as
today, remove_one will block until all ucontexts referring the device
are destroyed before returning.

The fourth patch provides implementation of this API for the mlx4
driver.

The last patch extends ucma to avoid blocking remove_one operation in
the cma module. When such device removal event is received, ucma is
turning all user contexts to zombie contexts. This is done by
releasing all underlying resources and preventing any further user
operations on the context.

Changes from V5:
Addressed Jason's comments for below patches:
patch #1: Improve kref usage.
patch #3: Use 2 different krefs for complete and memory, improve some comments.

Changes from V4:
patch #1,#3 - addressed Jason's comments.
patch #2, #4 - rebased upon last stuff.

Changes from V3:
Add 2 patches as a preparation for this series, details above.
patch #3: Change the locking schema based on Jason's comments.

Changes from V2:
patch #1: Rebase over ODP patches.

Changes from V1:
patch #1: Use uverbs flags instead of disassociate support, drop fatal_event_raised flag.
patch #3: Add support in ucma for handling device removal.

Changes from V0:
patch #1: ib_uverbs_close, reduced mutex scope to enable tasks run in parallel.
Yishai Hadas (5):
  IB/uverbs: Fix reference counting usage of event files
  IB/uverbs: Explicitly pass ib_dev to uverbs commands
  IB/uverbs: Enable device removal when there are active user space
    applications
  IB/mlx4_ib: Disassociate support
  IB/ucma: HW Device hot-removal support

 drivers/infiniband/core/ucma.c        |  130 +++++++++-
 drivers/infiniband/core/uverbs.h      |   16 +-
 drivers/infiniband/core/uverbs_cmd.c  |  114 ++++++----
 drivers/infiniband/core/uverbs_main.c |  438 +++++++++++++++++++++++++++------
 drivers/infiniband/hw/mlx4/main.c     |  139 ++++++++++-
 drivers/infiniband/hw/mlx4/mlx4_ib.h  |   13 +
 include/rdma/ib_verbs.h               |    1 +
 7 files changed, 714 insertions(+), 137 deletions(-)

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[PATCH for-next V6 1/5] IB/uverbs: Fix reference counting usage of event files

[Yishai Hadas]

Fix the reference counting usage to be handled in the event file
creation/destruction function, instead of being done by the caller.
This is done for both async/non-async event files.

Based on Jason Gunthorpe report at https://www.mail-archive.com/
linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org/msg24680.html:
"The existing code for this is broken, in ib_uverbs_get_context all
the error paths between ib_uverbs_alloc_event_file and the
kref_get(file->ref) are wrong - this will result in fput() which will
call ib_uverbs_event_close, which will try to do kref_put and
ib_unregister_event_handler - which are no longer paired."

Signed-off-by: Yishai Hadas <yishaih-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Signed-off-by: Shachar Raindel <raindel-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
---
 drivers/infiniband/core/uverbs.h      |    1 +
 drivers/infiniband/core/uverbs_cmd.c  |   11 +-------
 drivers/infiniband/core/uverbs_main.c |   44 ++++++++++++++++++++++++++++----
 3 files changed, 40 insertions(+), 16 deletions(-)

diff --git a/drivers/infiniband/core/uverbs.h b/drivers/infiniband/core/uverbs.h
index ba365b6..60e6e3d 100644
--- a/drivers/infiniband/core/uverbs.h
+++ b/drivers/infiniband/core/uverbs.h
@@ -178,6 +178,7 @@ void idr_remove_uobj(struct idr *idp, struct ib_uobject *uobj);
 
 struct file *ib_uverbs_alloc_event_file(struct ib_uverbs_file *uverbs_file,
 					int is_async);
+void ib_uverbs_free_async_event_file(struct ib_uverbs_file *uverbs_file);
 struct ib_uverbs_event_file *ib_uverbs_lookup_comp_file(int fd);
 
 void ib_uverbs_release_ucq(struct ib_uverbs_file *file,
diff --git a/drivers/infiniband/core/uverbs_cmd.c b/drivers/infiniband/core/uverbs_cmd.c
index bbb02ff..5720a92 100644
--- a/drivers/infiniband/core/uverbs_cmd.c
+++ b/drivers/infiniband/core/uverbs_cmd.c
@@ -367,16 +367,6 @@ ssize_t ib_uverbs_get_context(struct ib_uverbs_file *file,
 		goto err_file;
 	}
 
-	file->async_file = filp->private_data;
-
-	INIT_IB_EVENT_HANDLER(&file->event_handler, file->device->ib_dev,
-			      ib_uverbs_event_handler);
-	ret = ib_register_event_handler(&file->event_handler);
-	if (ret)
-		goto err_file;
-
-	kref_get(&file->async_file->ref);
-	kref_get(&file->ref);
 	file->ucontext = ucontext;
 
 	fd_install(resp.async_fd, filp);
@@ -386,6 +376,7 @@ ssize_t ib_uverbs_get_context(struct ib_uverbs_file *file,
 	return in_len;
 
 err_file:
+	ib_uverbs_free_async_event_file(file);
 	fput(filp);
 
 err_fd:
diff --git a/drivers/infiniband/core/uverbs_main.c b/drivers/infiniband/core/uverbs_main.c
index f6eef2d..c238eba 100644
--- a/drivers/infiniband/core/uverbs_main.c
+++ b/drivers/infiniband/core/uverbs_main.c
@@ -406,10 +406,9 @@ static int ib_uverbs_event_close(struct inode *inode, struct file *filp)
 	}
 	spin_unlock_irq(&file->lock);
 
-	if (file->is_async) {
+	if (file->is_async)
 		ib_unregister_event_handler(&file->uverbs_file->event_handler);
-		kref_put(&file->uverbs_file->ref, ib_uverbs_release_file);
-	}
+	kref_put(&file->uverbs_file->ref, ib_uverbs_release_file);
 	kref_put(&file->ref, ib_uverbs_release_event_file);
 
 	return 0;
@@ -541,13 +540,20 @@ void ib_uverbs_event_handler(struct ib_event_handler *handler,
 				NULL, NULL);
 }
 
+void ib_uverbs_free_async_event_file(struct ib_uverbs_file *file)
+{
+	kref_put(&file->async_file->ref, ib_uverbs_release_event_file);
+	file->async_file = NULL;
+}
+
 struct file *ib_uverbs_alloc_event_file(struct ib_uverbs_file *uverbs_file,
 					int is_async)
 {
 	struct ib_uverbs_event_file *ev_file;
 	struct file *filp;
+	int ret;
 
-	ev_file = kmalloc(sizeof *ev_file, GFP_KERNEL);
+	ev_file = kzalloc(sizeof(*ev_file), GFP_KERNEL);
 	if (!ev_file)
 		return ERR_PTR(-ENOMEM);
 
@@ -556,15 +562,41 @@ struct file *ib_uverbs_alloc_event_file(struct ib_uverbs_file *uverbs_file,
 	INIT_LIST_HEAD(&ev_file->event_list);
 	init_waitqueue_head(&ev_file->poll_wait);
 	ev_file->uverbs_file = uverbs_file;
+	kref_get(&ev_file->uverbs_file->ref);
 	ev_file->async_queue = NULL;
-	ev_file->is_async    = is_async;
 	ev_file->is_closed   = 0;
 
 	filp = anon_inode_getfile("[infinibandevent]", &uverbs_event_fops,
 				  ev_file, O_RDONLY);
 	if (IS_ERR(filp))
-		kfree(ev_file);
+		goto err_put_refs;
+
+	if (is_async) {
+		WARN_ON(uverbs_file->async_file);
+		uverbs_file->async_file = ev_file;
+		kref_get(&uverbs_file->async_file->ref);
+		INIT_IB_EVENT_HANDLER(&uverbs_file->event_handler,
+				      uverbs_file->device->ib_dev,
+				      ib_uverbs_event_handler);
+		ret = ib_register_event_handler(&uverbs_file->event_handler);
+		if (ret)
+			goto err_put_file;
+
+		/* At that point async file stuff was fully set */
+		ev_file->is_async = 1;
+	}
+
+	return filp;
+
+err_put_file:
+	fput(filp);
+	kref_put(&uverbs_file->async_file->ref, ib_uverbs_release_event_file);
+	uverbs_file->async_file = NULL;
+	return ERR_PTR(ret);
 
+err_put_refs:
+	kref_put(&ev_file->uverbs_file->ref, ib_uverbs_release_file);
+	kref_put(&ev_file->ref, ib_uverbs_release_event_file);
 	return filp;
 }
 
-- 
1.7.1

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Re: [PATCH for-next V6 1/5] IB/uverbs: Fix reference counting usage of event files

[Jason Gunthorpe]

On Tue, Jun 30, 2015 at 01:26:03PM +0300, Yishai Hadas wrote:

> Signed-off-by: Yishai Hadas <yishaih-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
> Signed-off-by: Shachar Raindel <raindel-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>

Reviewed-By: Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>

>  err_file:
> +	ib_uverbs_free_async_event_file(file);
>  	fput(filp);

> +void ib_uverbs_free_async_event_file(struct ib_uverbs_file *file)
> +{
> +	kref_put(&file->async_file->ref, ib_uverbs_release_event_file);
> +	file->async_file = NULL;
> +}

Mm, I figured out why that looks so wonky - there is no locking on the
async_file assign. Other cases were relying on
ib_register_event_handler not succeeding for locking, this doesn't
have that luxury. The async_file usage looks really weird overall,
there may be something strange there. But - that seems like a job for
another day..

Jason
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[PATCH for-next V6 2/5] IB/uverbs: Explicitly pass ib_dev to uverbs commands

[Yishai Hadas]

Done in preparation for deploying RCU for the device removal
flow. Allows isolating the RCU handling to the uverb_main layer and
keeping the uverbs_cmd code as is.

Signed-off-by: Yishai Hadas <yishaih-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Signed-off-by: Shachar Raindel <raindel-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
---
 drivers/infiniband/core/uverbs.h      |    3 +
 drivers/infiniband/core/uverbs_cmd.c  |  103 ++++++++++++++++++++++-----------
 drivers/infiniband/core/uverbs_main.c |   21 +++++--
 3 files changed, 88 insertions(+), 39 deletions(-)

diff --git a/drivers/infiniband/core/uverbs.h b/drivers/infiniband/core/uverbs.h
index 60e6e3d..dc002a1 100644
--- a/drivers/infiniband/core/uverbs.h
+++ b/drivers/infiniband/core/uverbs.h
@@ -177,6 +177,7 @@ extern struct idr ib_uverbs_rule_idr;
 void idr_remove_uobj(struct idr *idp, struct ib_uobject *uobj);
 
 struct file *ib_uverbs_alloc_event_file(struct ib_uverbs_file *uverbs_file,
+					struct ib_device *ib_dev,
 					int is_async);
 void ib_uverbs_free_async_event_file(struct ib_uverbs_file *uverbs_file);
 struct ib_uverbs_event_file *ib_uverbs_lookup_comp_file(int fd);
@@ -213,6 +214,7 @@ struct ib_uverbs_flow_spec {
 
 #define IB_UVERBS_DECLARE_CMD(name)					\
 	ssize_t ib_uverbs_##name(struct ib_uverbs_file *file,		\
+				 struct ib_device *ib_dev,              \
 				 const char __user *buf, int in_len,	\
 				 int out_len)
 
@@ -254,6 +256,7 @@ IB_UVERBS_DECLARE_CMD(close_xrcd);
 
 #define IB_UVERBS_DECLARE_EX_CMD(name)				\
 	int ib_uverbs_ex_##name(struct ib_uverbs_file *file,	\
+				struct ib_device *ib_dev,		\
 				struct ib_udata *ucore,		\
 				struct ib_udata *uhw)
 
diff --git a/drivers/infiniband/core/uverbs_cmd.c b/drivers/infiniband/core/uverbs_cmd.c
index 5720a92..29443c0 100644
--- a/drivers/infiniband/core/uverbs_cmd.c
+++ b/drivers/infiniband/core/uverbs_cmd.c
@@ -282,13 +282,13 @@ static void put_xrcd_read(struct ib_uobject *uobj)
 }
 
 ssize_t ib_uverbs_get_context(struct ib_uverbs_file *file,
+			      struct ib_device *ib_dev,
 			      const char __user *buf,
 			      int in_len, int out_len)
 {
 	struct ib_uverbs_get_context      cmd;
 	struct ib_uverbs_get_context_resp resp;
 	struct ib_udata                   udata;
-	struct ib_device                 *ibdev = file->device->ib_dev;
 #ifdef CONFIG_INFINIBAND_ON_DEMAND_PAGING
 	struct ib_device_attr		  dev_attr;
 #endif
@@ -313,13 +313,13 @@ ssize_t ib_uverbs_get_context(struct ib_uverbs_file *file,
 		   (unsigned long) cmd.response + sizeof resp,
 		   in_len - sizeof cmd, out_len - sizeof resp);
 
-	ucontext = ibdev->alloc_ucontext(ibdev, &udata);
+	ucontext = ib_dev->alloc_ucontext(ib_dev, &udata);
 	if (IS_ERR(ucontext)) {
 		ret = PTR_ERR(ucontext);
 		goto err;
 	}
 
-	ucontext->device = ibdev;
+	ucontext->device = ib_dev;
 	INIT_LIST_HEAD(&ucontext->pd_list);
 	INIT_LIST_HEAD(&ucontext->mr_list);
 	INIT_LIST_HEAD(&ucontext->mw_list);
@@ -340,7 +340,7 @@ ssize_t ib_uverbs_get_context(struct ib_uverbs_file *file,
 	ucontext->odp_mrs_count = 0;
 	INIT_LIST_HEAD(&ucontext->no_private_counters);
 
-	ret = ib_query_device(ibdev, &dev_attr);
+	ret = ib_query_device(ib_dev, &dev_attr);
 	if (ret)
 		goto err_free;
 	if (!(dev_attr.device_cap_flags & IB_DEVICE_ON_DEMAND_PAGING))
@@ -355,7 +355,7 @@ ssize_t ib_uverbs_get_context(struct ib_uverbs_file *file,
 		goto err_free;
 	resp.async_fd = ret;
 
-	filp = ib_uverbs_alloc_event_file(file, 1);
+	filp = ib_uverbs_alloc_event_file(file, ib_dev, 1);
 	if (IS_ERR(filp)) {
 		ret = PTR_ERR(filp);
 		goto err_fd;
@@ -384,7 +384,7 @@ err_fd:
 
 err_free:
 	put_pid(ucontext->tgid);
-	ibdev->dealloc_ucontext(ucontext);
+	ib_dev->dealloc_ucontext(ucontext);
 
 err:
 	mutex_unlock(&file->mutex);
@@ -392,11 +392,12 @@ err:
 }
 
 static void copy_query_dev_fields(struct ib_uverbs_file *file,
+				  struct ib_device *ib_dev,
 				  struct ib_uverbs_query_device_resp *resp,
 				  struct ib_device_attr *attr)
 {
 	resp->fw_ver		= attr->fw_ver;
-	resp->node_guid		= file->device->ib_dev->node_guid;
+	resp->node_guid		= ib_dev->node_guid;
 	resp->sys_image_guid	= attr->sys_image_guid;
 	resp->max_mr_size	= attr->max_mr_size;
 	resp->page_size_cap	= attr->page_size_cap;
@@ -434,10 +435,11 @@ static void copy_query_dev_fields(struct ib_uverbs_file *file,
 	resp->max_srq_sge		= attr->max_srq_sge;
 	resp->max_pkeys			= attr->max_pkeys;
 	resp->local_ca_ack_delay	= attr->local_ca_ack_delay;
-	resp->phys_port_cnt		= file->device->ib_dev->phys_port_cnt;
+	resp->phys_port_cnt		= ib_dev->phys_port_cnt;
 }
 
 ssize_t ib_uverbs_query_device(struct ib_uverbs_file *file,
+			       struct ib_device *ib_dev,
 			       const char __user *buf,
 			       int in_len, int out_len)
 {
@@ -452,12 +454,12 @@ ssize_t ib_uverbs_query_device(struct ib_uverbs_file *file,
 	if (copy_from_user(&cmd, buf, sizeof cmd))
 		return -EFAULT;
 
-	ret = ib_query_device(file->device->ib_dev, &attr);
+	ret = ib_query_device(ib_dev, &attr);
 	if (ret)
 		return ret;
 
 	memset(&resp, 0, sizeof resp);
-	copy_query_dev_fields(file, &resp, &attr);
+	copy_query_dev_fields(file, ib_dev, &resp, &attr);
 
 	if (copy_to_user((void __user *) (unsigned long) cmd.response,
 			 &resp, sizeof resp))
@@ -467,6 +469,7 @@ ssize_t ib_uverbs_query_device(struct ib_uverbs_file *file,
 }
 
 ssize_t ib_uverbs_query_port(struct ib_uverbs_file *file,
+			     struct ib_device *ib_dev,
 			     const char __user *buf,
 			     int in_len, int out_len)
 {
@@ -481,7 +484,7 @@ ssize_t ib_uverbs_query_port(struct ib_uverbs_file *file,
 	if (copy_from_user(&cmd, buf, sizeof cmd))
 		return -EFAULT;
 
-	ret = ib_query_port(file->device->ib_dev, cmd.port_num, &attr);
+	ret = ib_query_port(ib_dev, cmd.port_num, &attr);
 	if (ret)
 		return ret;
 
@@ -506,7 +509,7 @@ ssize_t ib_uverbs_query_port(struct ib_uverbs_file *file,
 	resp.active_width    = attr.active_width;
 	resp.active_speed    = attr.active_speed;
 	resp.phys_state      = attr.phys_state;
-	resp.link_layer      = rdma_port_get_link_layer(file->device->ib_dev,
+	resp.link_layer      = rdma_port_get_link_layer(ib_dev,
 							cmd.port_num);
 
 	if (copy_to_user((void __user *) (unsigned long) cmd.response,
@@ -517,6 +520,7 @@ ssize_t ib_uverbs_query_port(struct ib_uverbs_file *file,
 }
 
 ssize_t ib_uverbs_alloc_pd(struct ib_uverbs_file *file,
+			   struct ib_device *ib_dev,
 			   const char __user *buf,
 			   int in_len, int out_len)
 {
@@ -544,14 +548,13 @@ ssize_t ib_uverbs_alloc_pd(struct ib_uverbs_file *file,
 	init_uobj(uobj, 0, file->ucontext, &pd_lock_class);
 	down_write(&uobj->mutex);
 
-	pd = file->device->ib_dev->alloc_pd(file->device->ib_dev,
-					    file->ucontext, &udata);
+	pd = ib_dev->alloc_pd(ib_dev, file->ucontext, &udata);
 	if (IS_ERR(pd)) {
 		ret = PTR_ERR(pd);
 		goto err;
 	}
 
-	pd->device  = file->device->ib_dev;
+	pd->device  = ib_dev;
 	pd->uobject = uobj;
 	atomic_set(&pd->usecnt, 0);
 
@@ -591,6 +594,7 @@ err:
 }
 
 ssize_t ib_uverbs_dealloc_pd(struct ib_uverbs_file *file,
+			     struct ib_device *ib_dev,
 			     const char __user *buf,
 			     int in_len, int out_len)
 {
@@ -711,6 +715,7 @@ static void xrcd_table_delete(struct ib_uverbs_device *dev,
 }
 
 ssize_t ib_uverbs_open_xrcd(struct ib_uverbs_file *file,
+			    struct ib_device *ib_dev,
 			    const char __user *buf, int in_len,
 			    int out_len)
 {
@@ -769,15 +774,14 @@ ssize_t ib_uverbs_open_xrcd(struct ib_uverbs_file *file,
 	down_write(&obj->uobject.mutex);
 
 	if (!xrcd) {
-		xrcd = file->device->ib_dev->alloc_xrcd(file->device->ib_dev,
-							file->ucontext, &udata);
+		xrcd = ib_dev->alloc_xrcd(ib_dev, file->ucontext, &udata);
 		if (IS_ERR(xrcd)) {
 			ret = PTR_ERR(xrcd);
 			goto err;
 		}
 
 		xrcd->inode   = inode;
-		xrcd->device  = file->device->ib_dev;
+		xrcd->device  = ib_dev;
 		atomic_set(&xrcd->usecnt, 0);
 		mutex_init(&xrcd->tgt_qp_mutex);
 		INIT_LIST_HEAD(&xrcd->tgt_qp_list);
@@ -848,6 +852,7 @@ err_tree_mutex_unlock:
 }
 
 ssize_t ib_uverbs_close_xrcd(struct ib_uverbs_file *file,
+			     struct ib_device *ib_dev,
 			     const char __user *buf, int in_len,
 			     int out_len)
 {
@@ -925,6 +930,7 @@ void ib_uverbs_dealloc_xrcd(struct ib_uverbs_device *dev,
 }
 
 ssize_t ib_uverbs_reg_mr(struct ib_uverbs_file *file,
+			 struct ib_device *ib_dev,
 			 const char __user *buf, int in_len,
 			 int out_len)
 {
@@ -1034,6 +1040,7 @@ err_free:
 }
 
 ssize_t ib_uverbs_rereg_mr(struct ib_uverbs_file *file,
+			   struct ib_device *ib_dev,
 			   const char __user *buf, int in_len,
 			   int out_len)
 {
@@ -1127,6 +1134,7 @@ put_uobjs:
 }
 
 ssize_t ib_uverbs_dereg_mr(struct ib_uverbs_file *file,
+			   struct ib_device *ib_dev,
 			   const char __user *buf, int in_len,
 			   int out_len)
 {
@@ -1165,8 +1173,9 @@ ssize_t ib_uverbs_dereg_mr(struct ib_uverbs_file *file,
 }
 
 ssize_t ib_uverbs_alloc_mw(struct ib_uverbs_file *file,
-			 const char __user *buf, int in_len,
-			 int out_len)
+			   struct ib_device *ib_dev,
+			   const char __user *buf, int in_len,
+			   int out_len)
 {
 	struct ib_uverbs_alloc_mw      cmd;
 	struct ib_uverbs_alloc_mw_resp resp;
@@ -1247,8 +1256,9 @@ err_free:
 }
 
 ssize_t ib_uverbs_dealloc_mw(struct ib_uverbs_file *file,
-			   const char __user *buf, int in_len,
-			   int out_len)
+			     struct ib_device *ib_dev,
+			     const char __user *buf, int in_len,
+			     int out_len)
 {
 	struct ib_uverbs_dealloc_mw cmd;
 	struct ib_mw               *mw;
@@ -1285,6 +1295,7 @@ ssize_t ib_uverbs_dealloc_mw(struct ib_uverbs_file *file,
 }
 
 ssize_t ib_uverbs_create_comp_channel(struct ib_uverbs_file *file,
+				      struct ib_device *ib_dev,
 				      const char __user *buf, int in_len,
 				      int out_len)
 {
@@ -1304,7 +1315,7 @@ ssize_t ib_uverbs_create_comp_channel(struct ib_uverbs_file *file,
 		return ret;
 	resp.fd = ret;
 
-	filp = ib_uverbs_alloc_event_file(file, 0);
+	filp = ib_uverbs_alloc_event_file(file, ib_dev, 0);
 	if (IS_ERR(filp)) {
 		put_unused_fd(resp.fd);
 		return PTR_ERR(filp);
@@ -1322,6 +1333,7 @@ ssize_t ib_uverbs_create_comp_channel(struct ib_uverbs_file *file,
 }
 
 static struct ib_ucq_object *create_cq(struct ib_uverbs_file *file,
+					struct ib_device *ib_dev,
 				       struct ib_udata *ucore,
 				       struct ib_udata *uhw,
 				       struct ib_uverbs_ex_create_cq *cmd,
@@ -1370,14 +1382,14 @@ static struct ib_ucq_object *create_cq(struct ib_uverbs_file *file,
 	if (cmd_sz > offsetof(typeof(*cmd), flags) + sizeof(cmd->flags))
 		attr.flags = cmd->flags;
 
-	cq = file->device->ib_dev->create_cq(file->device->ib_dev, &attr,
+	cq = ib_dev->create_cq(ib_dev, &attr,
 					     file->ucontext, uhw);
 	if (IS_ERR(cq)) {
 		ret = PTR_ERR(cq);
 		goto err_file;
 	}
 
-	cq->device        = file->device->ib_dev;
+	cq->device        = ib_dev;
 	cq->uobject       = &obj->uobject;
 	cq->comp_handler  = ib_uverbs_comp_handler;
 	cq->event_handler = ib_uverbs_cq_event_handler;
@@ -1438,6 +1450,7 @@ static int ib_uverbs_create_cq_cb(struct ib_uverbs_file *file,
 }
 
 ssize_t ib_uverbs_create_cq(struct ib_uverbs_file *file,
+			    struct ib_device *ib_dev,
 			    const char __user *buf, int in_len,
 			    int out_len)
 {
@@ -1466,7 +1479,7 @@ ssize_t ib_uverbs_create_cq(struct ib_uverbs_file *file,
 	cmd_ex.comp_vector = cmd.comp_vector;
 	cmd_ex.comp_channel = cmd.comp_channel;
 
-	obj = create_cq(file, &ucore, &uhw, &cmd_ex,
+	obj = create_cq(file, ib_dev, &ucore, &uhw, &cmd_ex,
 			offsetof(typeof(cmd_ex), comp_channel) +
 			sizeof(cmd.comp_channel), ib_uverbs_create_cq_cb,
 			NULL);
@@ -1489,6 +1502,7 @@ static int ib_uverbs_ex_create_cq_cb(struct ib_uverbs_file *file,
 }
 
 int ib_uverbs_ex_create_cq(struct ib_uverbs_file *file,
+			 struct ib_device *ib_dev,
 			   struct ib_udata *ucore,
 			   struct ib_udata *uhw)
 {
@@ -1514,7 +1528,7 @@ int ib_uverbs_ex_create_cq(struct ib_uverbs_file *file,
 			     sizeof(resp.response_length)))
 		return -ENOSPC;
 
-	obj = create_cq(file, ucore, uhw, &cmd,
+	obj = create_cq(file, ib_dev, ucore, uhw, &cmd,
 			min(ucore->inlen, sizeof(cmd)),
 			ib_uverbs_ex_create_cq_cb, NULL);
 
@@ -1525,6 +1539,7 @@ int ib_uverbs_ex_create_cq(struct ib_uverbs_file *file,
 }
 
 ssize_t ib_uverbs_resize_cq(struct ib_uverbs_file *file,
+			    struct ib_device *ib_dev,
 			    const char __user *buf, int in_len,
 			    int out_len)
 {
@@ -1588,6 +1603,7 @@ static int copy_wc_to_user(void __user *dest, struct ib_wc *wc)
 }
 
 ssize_t ib_uverbs_poll_cq(struct ib_uverbs_file *file,
+			  struct ib_device *ib_dev,
 			  const char __user *buf, int in_len,
 			  int out_len)
 {
@@ -1639,6 +1655,7 @@ out_put:
 }
 
 ssize_t ib_uverbs_req_notify_cq(struct ib_uverbs_file *file,
+				struct ib_device *ib_dev,
 				const char __user *buf, int in_len,
 				int out_len)
 {
@@ -1661,6 +1678,7 @@ ssize_t ib_uverbs_req_notify_cq(struct ib_uverbs_file *file,
 }
 
 ssize_t ib_uverbs_destroy_cq(struct ib_uverbs_file *file,
+			     struct ib_device *ib_dev,
 			     const char __user *buf, int in_len,
 			     int out_len)
 {
@@ -1713,6 +1731,7 @@ ssize_t ib_uverbs_destroy_cq(struct ib_uverbs_file *file,
 }
 
 ssize_t ib_uverbs_create_qp(struct ib_uverbs_file *file,
+			    struct ib_device *ib_dev,
 			    const char __user *buf, int in_len,
 			    int out_len)
 {
@@ -1908,6 +1927,7 @@ err_put:
 }
 
 ssize_t ib_uverbs_open_qp(struct ib_uverbs_file *file,
+			  struct ib_device *ib_dev,
 			  const char __user *buf, int in_len, int out_len)
 {
 	struct ib_uverbs_open_qp        cmd;
@@ -2002,6 +2022,7 @@ err_put:
 }
 
 ssize_t ib_uverbs_query_qp(struct ib_uverbs_file *file,
+			   struct ib_device *ib_dev,
 			   const char __user *buf, int in_len,
 			   int out_len)
 {
@@ -2116,6 +2137,7 @@ static int modify_qp_mask(enum ib_qp_type qp_type, int mask)
 }
 
 ssize_t ib_uverbs_modify_qp(struct ib_uverbs_file *file,
+			    struct ib_device *ib_dev,
 			    const char __user *buf, int in_len,
 			    int out_len)
 {
@@ -2212,6 +2234,7 @@ out:
 }
 
 ssize_t ib_uverbs_destroy_qp(struct ib_uverbs_file *file,
+			     struct ib_device *ib_dev,
 			     const char __user *buf, int in_len,
 			     int out_len)
 {
@@ -2270,6 +2293,7 @@ ssize_t ib_uverbs_destroy_qp(struct ib_uverbs_file *file,
 }
 
 ssize_t ib_uverbs_post_send(struct ib_uverbs_file *file,
+			    struct ib_device *ib_dev,
 			    const char __user *buf, int in_len,
 			    int out_len)
 {
@@ -2514,6 +2538,7 @@ err:
 }
 
 ssize_t ib_uverbs_post_recv(struct ib_uverbs_file *file,
+			    struct ib_device *ib_dev,
 			    const char __user *buf, int in_len,
 			    int out_len)
 {
@@ -2563,6 +2588,7 @@ out:
 }
 
 ssize_t ib_uverbs_post_srq_recv(struct ib_uverbs_file *file,
+				struct ib_device *ib_dev,
 				const char __user *buf, int in_len,
 				int out_len)
 {
@@ -2612,6 +2638,7 @@ out:
 }
 
 ssize_t ib_uverbs_create_ah(struct ib_uverbs_file *file,
+			    struct ib_device *ib_dev,
 			    const char __user *buf, int in_len,
 			    int out_len)
 {
@@ -2704,6 +2731,7 @@ err:
 }
 
 ssize_t ib_uverbs_destroy_ah(struct ib_uverbs_file *file,
+			     struct ib_device *ib_dev,
 			     const char __user *buf, int in_len, int out_len)
 {
 	struct ib_uverbs_destroy_ah cmd;
@@ -2740,6 +2768,7 @@ ssize_t ib_uverbs_destroy_ah(struct ib_uverbs_file *file,
 }
 
 ssize_t ib_uverbs_attach_mcast(struct ib_uverbs_file *file,
+			       struct ib_device *ib_dev,
 			       const char __user *buf, int in_len,
 			       int out_len)
 {
@@ -2787,6 +2816,7 @@ out_put:
 }
 
 ssize_t ib_uverbs_detach_mcast(struct ib_uverbs_file *file,
+			       struct ib_device *ib_dev,
 			       const char __user *buf, int in_len,
 			       int out_len)
 {
@@ -2867,6 +2897,7 @@ static int kern_spec_to_ib_spec(struct ib_uverbs_flow_spec *kern_spec,
 }
 
 int ib_uverbs_ex_create_flow(struct ib_uverbs_file *file,
+			     struct ib_device *ib_dev,
 			     struct ib_udata *ucore,
 			     struct ib_udata *uhw)
 {
@@ -3027,6 +3058,7 @@ err_free_attr:
 }
 
 int ib_uverbs_ex_destroy_flow(struct ib_uverbs_file *file,
+			      struct ib_device *ib_dev,
 			      struct ib_udata *ucore,
 			      struct ib_udata *uhw)
 {
@@ -3069,6 +3101,7 @@ int ib_uverbs_ex_destroy_flow(struct ib_uverbs_file *file,
 }
 
 static int __uverbs_create_xsrq(struct ib_uverbs_file *file,
+				struct ib_device *ib_dev,
 				struct ib_uverbs_create_xsrq *cmd,
 				struct ib_udata *udata)
 {
@@ -3202,6 +3235,7 @@ err:
 }
 
 ssize_t ib_uverbs_create_srq(struct ib_uverbs_file *file,
+			     struct ib_device *ib_dev,
 			     const char __user *buf, int in_len,
 			     int out_len)
 {
@@ -3229,7 +3263,7 @@ ssize_t ib_uverbs_create_srq(struct ib_uverbs_file *file,
 		   (unsigned long) cmd.response + sizeof resp,
 		   in_len - sizeof cmd, out_len - sizeof resp);
 
-	ret = __uverbs_create_xsrq(file, &xcmd, &udata);
+	ret = __uverbs_create_xsrq(file, ib_dev, &xcmd, &udata);
 	if (ret)
 		return ret;
 
@@ -3237,6 +3271,7 @@ ssize_t ib_uverbs_create_srq(struct ib_uverbs_file *file,
 }
 
 ssize_t ib_uverbs_create_xsrq(struct ib_uverbs_file *file,
+			      struct ib_device *ib_dev,
 			      const char __user *buf, int in_len, int out_len)
 {
 	struct ib_uverbs_create_xsrq     cmd;
@@ -3254,7 +3289,7 @@ ssize_t ib_uverbs_create_xsrq(struct ib_uverbs_file *file,
 		   (unsigned long) cmd.response + sizeof resp,
 		   in_len - sizeof cmd, out_len - sizeof resp);
 
-	ret = __uverbs_create_xsrq(file, &cmd, &udata);
+	ret = __uverbs_create_xsrq(file, ib_dev, &cmd, &udata);
 	if (ret)
 		return ret;
 
@@ -3262,6 +3297,7 @@ ssize_t ib_uverbs_create_xsrq(struct ib_uverbs_file *file,
 }
 
 ssize_t ib_uverbs_modify_srq(struct ib_uverbs_file *file,
+			     struct ib_device *ib_dev,
 			     const char __user *buf, int in_len,
 			     int out_len)
 {
@@ -3292,6 +3328,7 @@ ssize_t ib_uverbs_modify_srq(struct ib_uverbs_file *file,
 }
 
 ssize_t ib_uverbs_query_srq(struct ib_uverbs_file *file,
+			    struct ib_device *ib_dev,
 			    const char __user *buf,
 			    int in_len, int out_len)
 {
@@ -3332,6 +3369,7 @@ ssize_t ib_uverbs_query_srq(struct ib_uverbs_file *file,
 }
 
 ssize_t ib_uverbs_destroy_srq(struct ib_uverbs_file *file,
+			      struct ib_device *ib_dev,
 			      const char __user *buf, int in_len,
 			      int out_len)
 {
@@ -3389,16 +3427,15 @@ ssize_t ib_uverbs_destroy_srq(struct ib_uverbs_file *file,
 }
 
 int ib_uverbs_ex_query_device(struct ib_uverbs_file *file,
+			      struct ib_device *ib_dev,
 			      struct ib_udata *ucore,
 			      struct ib_udata *uhw)
 {
 	struct ib_uverbs_ex_query_device_resp resp;
 	struct ib_uverbs_ex_query_device  cmd;
 	struct ib_device_attr attr;
-	struct ib_device *device;
 	int err;
 
-	device = file->device->ib_dev;
 	if (ucore->inlen < sizeof(cmd))
 		return -EINVAL;
 
@@ -3419,11 +3456,11 @@ int ib_uverbs_ex_query_device(struct ib_uverbs_file *file,
 
 	memset(&attr, 0, sizeof(attr));
 
-	err = device->query_device(device, &attr, uhw);
+	err = ib_dev->query_device(ib_dev, &attr, uhw);
 	if (err)
 		return err;
 
-	copy_query_dev_fields(file, &resp.base, &attr);
+	copy_query_dev_fields(file, ib_dev, &resp.base, &attr);
 	resp.comp_mask = 0;
 
 	if (ucore->outlen < resp.response_length + sizeof(resp.odp_caps))
diff --git a/drivers/infiniband/core/uverbs_main.c b/drivers/infiniband/core/uverbs_main.c
index c238eba..e8dbabf 100644
--- a/drivers/infiniband/core/uverbs_main.c
+++ b/drivers/infiniband/core/uverbs_main.c
@@ -79,6 +79,7 @@ static DEFINE_SPINLOCK(map_lock);
 static DECLARE_BITMAP(dev_map, IB_UVERBS_MAX_DEVICES);
 
 static ssize_t (*uverbs_cmd_table[])(struct ib_uverbs_file *file,
+				     struct ib_device *ib_dev,
 				     const char __user *buf, int in_len,
 				     int out_len) = {
 	[IB_USER_VERBS_CMD_GET_CONTEXT]		= ib_uverbs_get_context,
@@ -119,6 +120,7 @@ static ssize_t (*uverbs_cmd_table[])(struct ib_uverbs_file *file,
 };
 
 static int (*uverbs_ex_cmd_table[])(struct ib_uverbs_file *file,
+				    struct ib_device *ib_dev,
 				    struct ib_udata *ucore,
 				    struct ib_udata *uhw) = {
 	[IB_USER_VERBS_EX_CMD_CREATE_FLOW]	= ib_uverbs_ex_create_flow,
@@ -547,6 +549,7 @@ void ib_uverbs_free_async_event_file(struct ib_uverbs_file *file)
 }
 
 struct file *ib_uverbs_alloc_event_file(struct ib_uverbs_file *uverbs_file,
+					struct ib_device	*ib_dev,
 					int is_async)
 {
 	struct ib_uverbs_event_file *ev_file;
@@ -576,7 +579,7 @@ struct file *ib_uverbs_alloc_event_file(struct ib_uverbs_file *uverbs_file,
 		uverbs_file->async_file = ev_file;
 		kref_get(&uverbs_file->async_file->ref);
 		INIT_IB_EVENT_HANDLER(&uverbs_file->event_handler,
-				      uverbs_file->device->ib_dev,
+				      ib_dev,
 				      ib_uverbs_event_handler);
 		ret = ib_register_event_handler(&uverbs_file->event_handler);
 		if (ret)
@@ -633,9 +636,13 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
 			     size_t count, loff_t *pos)
 {
 	struct ib_uverbs_file *file = filp->private_data;
+	struct ib_device *ib_dev = file->device->ib_dev;
 	struct ib_uverbs_cmd_hdr hdr;
 	__u32 flags;
 
+	if (!ib_dev)
+		return -ENODEV;
+
 	if (count < sizeof hdr)
 		return -EINVAL;
 
@@ -662,13 +669,13 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
 		    command != IB_USER_VERBS_CMD_GET_CONTEXT)
 			return -EINVAL;
 
-		if (!(file->device->ib_dev->uverbs_cmd_mask & (1ull << command)))
+		if (!(ib_dev->uverbs_cmd_mask & (1ull << command)))
 			return -ENOSYS;
 
 		if (hdr.in_words * 4 != count)
 			return -EINVAL;
 
-		return uverbs_cmd_table[command](file,
+		return uverbs_cmd_table[command](file, ib_dev,
 						 buf + sizeof(hdr),
 						 hdr.in_words * 4,
 						 hdr.out_words * 4);
@@ -695,7 +702,7 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
 		if (!file->ucontext)
 			return -EINVAL;
 
-		if (!(file->device->ib_dev->uverbs_ex_cmd_mask & (1ull << command)))
+		if (!(ib_dev->uverbs_ex_cmd_mask & (1ull << command)))
 			return -ENOSYS;
 
 		if (count < (sizeof(hdr) + sizeof(ex_hdr)))
@@ -736,6 +743,7 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
 				       ex_hdr.provider_out_words * 8);
 
 		err = uverbs_ex_cmd_table[command](file,
+						   ib_dev,
 						   &ucore,
 						   &uhw);
 
@@ -751,11 +759,12 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
 static int ib_uverbs_mmap(struct file *filp, struct vm_area_struct *vma)
 {
 	struct ib_uverbs_file *file = filp->private_data;
+	struct ib_device *ib_dev = file->device->ib_dev;
 
-	if (!file->ucontext)
+	if (!ib_dev || !file->ucontext)
 		return -ENODEV;
 	else
-		return file->device->ib_dev->mmap(file->ucontext, vma);
+		return ib_dev->mmap(file->ucontext, vma);
 }
 
 /*
-- 
1.7.1

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Re: [PATCH for-next V6 2/5] IB/uverbs: Explicitly pass ib_dev to uverbs commands

[Jason Gunthorpe]

On Tue, Jun 30, 2015 at 01:26:04PM +0300, Yishai Hadas wrote:
> Done in preparation for deploying RCU for the device removal
> flow. Allows isolating the RCU handling to the uverb_main layer and
> keeping the uverbs_cmd code as is.
> 
> Signed-off-by: Yishai Hadas <yishaih-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
> Signed-off-by: Shachar Raindel <raindel-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>

Reviewed-By: Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>

Jason
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[PATCH for-next V6 3/5] IB/uverbs: Enable device removal when there are active user space applications

[Yishai Hadas]

Enables the uverbs_remove_one to succeed despite the fact that there are
running IB applications working with the given ib device.  This functionality
enables a HW device to be unbind/reset despite the fact that there are running
user space applications using it.

It exposes a new IB kernel API named 'disassociate_ucontext' which lets a
driver detaching its HW resources from a given user context without
crashing/terminating the application. In case a driver implemented the above
API and registered with ib_uverb there will be no dependency between its device
to its uverbs_device. Upon calling remove_one of ib_uverbs the call should
return after disassociating the open HW resources without waiting to clients
disconnecting. In case driver didn't implement this API there will be no change
to current behaviour and uverbs_remove_one will return only when last client
has disconnected and reference count on uverbs device became 0.

In case the lower driver device was removed any application will continue
working over some zombie HCA, further calls will ended with an immediate error.

Signed-off-by: Yishai Hadas <yishaih-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Signed-off-by: Shachar Raindel <raindel-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
---
 drivers/infiniband/core/uverbs.h      |   12 +-
 drivers/infiniband/core/uverbs_main.c |  399 ++++++++++++++++++++++++++-------
 include/rdma/ib_verbs.h               |    1 +
 3 files changed, 330 insertions(+), 82 deletions(-)

diff --git a/drivers/infiniband/core/uverbs.h b/drivers/infiniband/core/uverbs.h
index dc002a1..ef1cd7e 100644
--- a/drivers/infiniband/core/uverbs.h
+++ b/drivers/infiniband/core/uverbs.h
@@ -85,15 +85,20 @@
  */
 
 struct ib_uverbs_device {
-	struct kref				ref;
+	struct kref				comp_ref;
+	struct kref				free_ref;
 	int					num_comp_vectors;
 	struct completion			comp;
 	struct device			       *dev;
-	struct ib_device		       *ib_dev;
+	struct ib_device	__rcu	       *ib_dev;
 	int					devnum;
 	struct cdev			        cdev;
 	struct rb_root				xrcd_tree;
 	struct mutex				xrcd_tree_mutex;
+	struct srcu_struct			disassociate_srcu;
+	struct mutex				lists_mutex; /* protect lists */
+	struct list_head			uverbs_file_list;
+	struct list_head			uverbs_events_file_list;
 };
 
 struct ib_uverbs_event_file {
@@ -105,6 +110,7 @@ struct ib_uverbs_event_file {
 	wait_queue_head_t			poll_wait;
 	struct fasync_struct		       *async_queue;
 	struct list_head			event_list;
+	struct list_head			list;
 };
 
 struct ib_uverbs_file {
@@ -114,6 +120,8 @@ struct ib_uverbs_file {
 	struct ib_ucontext		       *ucontext;
 	struct ib_event_handler			event_handler;
 	struct ib_uverbs_event_file	       *async_file;
+	struct list_head			list;
+	int					is_closed;
 };
 
 struct ib_uverbs_event {
diff --git a/drivers/infiniband/core/uverbs_main.c b/drivers/infiniband/core/uverbs_main.c
index e8dbabf..d7a2c30 100644
--- a/drivers/infiniband/core/uverbs_main.c
+++ b/drivers/infiniband/core/uverbs_main.c
@@ -132,14 +132,23 @@ static int (*uverbs_ex_cmd_table[])(struct ib_uverbs_file *file,
 static void ib_uverbs_add_one(struct ib_device *device);
 static void ib_uverbs_remove_one(struct ib_device *device);
 
-static void ib_uverbs_release_dev(struct kref *ref)
+static void ib_uverbs_comp_dev(struct kref *ref)
 {
 	struct ib_uverbs_device *dev =
-		container_of(ref, struct ib_uverbs_device, ref);
+		container_of(ref, struct ib_uverbs_device, comp_ref);
 
 	complete(&dev->comp);
 }
 
+static void ib_uverbs_release_dev(struct kref *ref)
+{
+	struct ib_uverbs_device *dev =
+		container_of(ref, struct ib_uverbs_device, free_ref);
+
+	cleanup_srcu_struct(&dev->disassociate_srcu);
+	kfree(dev);
+}
+
 static void ib_uverbs_release_event_file(struct kref *ref)
 {
 	struct ib_uverbs_event_file *file =
@@ -203,9 +212,6 @@ static int ib_uverbs_cleanup_ucontext(struct ib_uverbs_file *file,
 {
 	struct ib_uobject *uobj, *tmp;
 
-	if (!context)
-		return 0;
-
 	context->closing = 1;
 
 	list_for_each_entry_safe(uobj, tmp, &context->ah_list, list) {
@@ -309,9 +315,17 @@ static void ib_uverbs_release_file(struct kref *ref)
 {
 	struct ib_uverbs_file *file =
 		container_of(ref, struct ib_uverbs_file, ref);
-
-	module_put(file->device->ib_dev->owner);
-	kref_put(&file->device->ref, ib_uverbs_release_dev);
+	struct ib_device *ib_dev;
+	int srcu_key;
+
+	srcu_key = srcu_read_lock(&file->device->disassociate_srcu);
+	ib_dev = srcu_dereference(file->device->ib_dev,
+				  &file->device->disassociate_srcu);
+	if (ib_dev && !ib_dev->disassociate_ucontext)
+		module_put(ib_dev->owner);
+	srcu_read_unlock(&file->device->disassociate_srcu, srcu_key);
+	kref_put(&file->device->comp_ref, ib_uverbs_comp_dev);
+	kref_put(&file->device->free_ref, ib_uverbs_release_dev);
 
 	kfree(file);
 }
@@ -333,9 +347,19 @@ static ssize_t ib_uverbs_event_read(struct file *filp, char __user *buf,
 			return -EAGAIN;
 
 		if (wait_event_interruptible(file->poll_wait,
-					     !list_empty(&file->event_list)))
+					     (!list_empty(&file->event_list) ||
+			/* The barriers built into wait_event_interruptible()
+			 * and wake_up() guarentee this will see the null set
+			 * without using RCU
+			 */
+					     !file->uverbs_file->device->ib_dev)))
 			return -ERESTARTSYS;
 
+		/* If device was disassociated and no event exists set an error */
+		if (list_empty(&file->event_list) &&
+		    !file->uverbs_file->device->ib_dev)
+			return -EIO;
+
 		spin_lock_irq(&file->lock);
 	}
 
@@ -398,8 +422,11 @@ static int ib_uverbs_event_close(struct inode *inode, struct file *filp)
 {
 	struct ib_uverbs_event_file *file = filp->private_data;
 	struct ib_uverbs_event *entry, *tmp;
+	int closed_already = 0;
 
+	mutex_lock(&file->uverbs_file->device->lists_mutex);
 	spin_lock_irq(&file->lock);
+	closed_already = file->is_closed;
 	file->is_closed = 1;
 	list_for_each_entry_safe(entry, tmp, &file->event_list, list) {
 		if (entry->counter)
@@ -407,9 +434,14 @@ static int ib_uverbs_event_close(struct inode *inode, struct file *filp)
 		kfree(entry);
 	}
 	spin_unlock_irq(&file->lock);
+	if (!closed_already) {
+		list_del(&file->list);
+		if (file->is_async)
+			ib_unregister_event_handler(&file->uverbs_file->
+				event_handler);
+	}
+	mutex_unlock(&file->uverbs_file->device->lists_mutex);
 
-	if (file->is_async)
-		ib_unregister_event_handler(&file->uverbs_file->event_handler);
 	kref_put(&file->uverbs_file->ref, ib_uverbs_release_file);
 	kref_put(&file->ref, ib_uverbs_release_event_file);
 
@@ -574,6 +606,11 @@ struct file *ib_uverbs_alloc_event_file(struct ib_uverbs_file *uverbs_file,
 	if (IS_ERR(filp))
 		goto err_put_refs;
 
+	mutex_lock(&uverbs_file->device->lists_mutex);
+	list_add_tail(&ev_file->list,
+		      &uverbs_file->device->uverbs_events_file_list);
+	mutex_unlock(&uverbs_file->device->lists_mutex);
+
 	if (is_async) {
 		WARN_ON(uverbs_file->async_file);
 		uverbs_file->async_file = ev_file;
@@ -636,12 +673,11 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
 			     size_t count, loff_t *pos)
 {
 	struct ib_uverbs_file *file = filp->private_data;
-	struct ib_device *ib_dev = file->device->ib_dev;
+	struct ib_device *ib_dev;
 	struct ib_uverbs_cmd_hdr hdr;
 	__u32 flags;
-
-	if (!ib_dev)
-		return -ENODEV;
+	int srcu_key;
+	ssize_t ret;
 
 	if (count < sizeof hdr)
 		return -EINVAL;
@@ -649,6 +685,14 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
 	if (copy_from_user(&hdr, buf, sizeof hdr))
 		return -EFAULT;
 
+	srcu_key = srcu_read_lock(&file->device->disassociate_srcu);
+	ib_dev = srcu_dereference(file->device->ib_dev,
+				  &file->device->disassociate_srcu);
+	if (!ib_dev) {
+		ret = -EIO;
+		goto out;
+	}
+
 	flags = (hdr.command &
 		 IB_USER_VERBS_CMD_FLAGS_MASK) >> IB_USER_VERBS_CMD_FLAGS_SHIFT;
 
@@ -656,26 +700,36 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
 		__u32 command;
 
 		if (hdr.command & ~(__u32)(IB_USER_VERBS_CMD_FLAGS_MASK |
-					   IB_USER_VERBS_CMD_COMMAND_MASK))
-			return -EINVAL;
+					   IB_USER_VERBS_CMD_COMMAND_MASK)) {
+			ret = -EINVAL;
+			goto out;
+		}
 
 		command = hdr.command & IB_USER_VERBS_CMD_COMMAND_MASK;
 
 		if (command >= ARRAY_SIZE(uverbs_cmd_table) ||
-		    !uverbs_cmd_table[command])
-			return -EINVAL;
+		    !uverbs_cmd_table[command]) {
+			ret = -EINVAL;
+			goto out;
+		}
 
 		if (!file->ucontext &&
-		    command != IB_USER_VERBS_CMD_GET_CONTEXT)
-			return -EINVAL;
+		    command != IB_USER_VERBS_CMD_GET_CONTEXT) {
+			ret = -EINVAL;
+			goto out;
+		}
 
-		if (!(ib_dev->uverbs_cmd_mask & (1ull << command)))
-			return -ENOSYS;
+		if (!(ib_dev->uverbs_cmd_mask & (1ull << command))) {
+			ret = -ENOSYS;
+			goto out;
+		}
 
-		if (hdr.in_words * 4 != count)
-			return -EINVAL;
+		if (hdr.in_words * 4 != count) {
+			ret = -EINVAL;
+			goto out;
+		}
 
-		return uverbs_cmd_table[command](file, ib_dev,
+		ret = uverbs_cmd_table[command](file, ib_dev,
 						 buf + sizeof(hdr),
 						 hdr.in_words * 4,
 						 hdr.out_words * 4);
@@ -686,51 +740,72 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
 		struct ib_uverbs_ex_cmd_hdr ex_hdr;
 		struct ib_udata ucore;
 		struct ib_udata uhw;
-		int err;
 		size_t written_count = count;
 
 		if (hdr.command & ~(__u32)(IB_USER_VERBS_CMD_FLAGS_MASK |
-					   IB_USER_VERBS_CMD_COMMAND_MASK))
-			return -EINVAL;
+					   IB_USER_VERBS_CMD_COMMAND_MASK)) {
+			ret = -EINVAL;
+			goto out;
+		}
 
 		command = hdr.command & IB_USER_VERBS_CMD_COMMAND_MASK;
 
 		if (command >= ARRAY_SIZE(uverbs_ex_cmd_table) ||
-		    !uverbs_ex_cmd_table[command])
-			return -ENOSYS;
+		    !uverbs_ex_cmd_table[command]) {
+			ret = -ENOSYS;
+			goto out;
+		}
 
-		if (!file->ucontext)
-			return -EINVAL;
+		if (!file->ucontext) {
+			ret = -EINVAL;
+			goto out;
+		}
 
-		if (!(ib_dev->uverbs_ex_cmd_mask & (1ull << command)))
-			return -ENOSYS;
+		if (!(ib_dev->uverbs_ex_cmd_mask & (1ull << command))) {
+			ret = -ENOSYS;
+			goto out;
+		}
 
-		if (count < (sizeof(hdr) + sizeof(ex_hdr)))
-			return -EINVAL;
+		if (count < (sizeof(hdr) + sizeof(ex_hdr))) {
+			ret = -EINVAL;
+			goto out;
+		}
 
-		if (copy_from_user(&ex_hdr, buf + sizeof(hdr), sizeof(ex_hdr)))
-			return -EFAULT;
+		if (copy_from_user(&ex_hdr, buf + sizeof(hdr), sizeof(ex_hdr))) {
+			ret = -EFAULT;
+			goto out;
+		}
 
 		count -= sizeof(hdr) + sizeof(ex_hdr);
 		buf += sizeof(hdr) + sizeof(ex_hdr);
 
-		if ((hdr.in_words + ex_hdr.provider_in_words) * 8 != count)
-			return -EINVAL;
+		if ((hdr.in_words + ex_hdr.provider_in_words) * 8 != count) {
+			ret = -EINVAL;
+			goto out;
+		}
 
-		if (ex_hdr.cmd_hdr_reserved)
-			return -EINVAL;
+		if (ex_hdr.cmd_hdr_reserved) {
+			ret = -EINVAL;
+			goto out;
+		}
 
 		if (ex_hdr.response) {
-			if (!hdr.out_words && !ex_hdr.provider_out_words)
-				return -EINVAL;
+			if (!hdr.out_words && !ex_hdr.provider_out_words) {
+				ret = -EINVAL;
+				goto out;
+			}
 
 			if (!access_ok(VERIFY_WRITE,
 				       (void __user *) (unsigned long) ex_hdr.response,
-				       (hdr.out_words + ex_hdr.provider_out_words) * 8))
-				return -EFAULT;
+				       (hdr.out_words + ex_hdr.provider_out_words) * 8)) {
+				ret = -EFAULT;
+				goto out;
+			}
 		} else {
-			if (hdr.out_words || ex_hdr.provider_out_words)
-				return -EINVAL;
+			if (hdr.out_words || ex_hdr.provider_out_words) {
+				ret = -EINVAL;
+				goto out;
+			}
 		}
 
 		INIT_UDATA_BUF_OR_NULL(&ucore, buf, (unsigned long) ex_hdr.response,
@@ -742,29 +817,43 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
 				       ex_hdr.provider_in_words * 8,
 				       ex_hdr.provider_out_words * 8);
 
-		err = uverbs_ex_cmd_table[command](file,
+		ret = uverbs_ex_cmd_table[command](file,
 						   ib_dev,
 						   &ucore,
 						   &uhw);
-
-		if (err)
-			return err;
-
-		return written_count;
+		if (!ret)
+			ret = written_count;
+	} else {
+		ret = -ENOSYS;
 	}
 
-	return -ENOSYS;
+out:
+	srcu_read_unlock(&file->device->disassociate_srcu, srcu_key);
+	return ret;
 }
 
 static int ib_uverbs_mmap(struct file *filp, struct vm_area_struct *vma)
 {
 	struct ib_uverbs_file *file = filp->private_data;
-	struct ib_device *ib_dev = file->device->ib_dev;
+	struct ib_device *ib_dev;
+	int ret = 0;
+	int srcu_key;
 
-	if (!ib_dev || !file->ucontext)
-		return -ENODEV;
+	srcu_key = srcu_read_lock(&file->device->disassociate_srcu);
+	ib_dev = srcu_dereference(file->device->ib_dev,
+				  &file->device->disassociate_srcu);
+	if (!ib_dev) {
+		ret = -EIO;
+		goto out;
+	}
+
+	if (!file->ucontext)
+		ret = -ENODEV;
 	else
-		return ib_dev->mmap(file->ucontext, vma);
+		ret = ib_dev->mmap(file->ucontext, vma);
+out:
+	srcu_read_unlock(&file->device->disassociate_srcu, srcu_key);
+	return ret;
 }
 
 /*
@@ -781,23 +870,47 @@ static int ib_uverbs_open(struct inode *inode, struct file *filp)
 {
 	struct ib_uverbs_device *dev;
 	struct ib_uverbs_file *file;
+	struct ib_device *ib_dev;
 	int ret;
+	int module_dependent;
+	int srcu_key;
 
 	dev = container_of(inode->i_cdev, struct ib_uverbs_device, cdev);
-	if (dev)
-		kref_get(&dev->ref);
-	else
+	if (dev) {
+		kref_get(&dev->comp_ref);
+		kref_get(&dev->free_ref);
+	} else {
 		return -ENXIO;
+	}
 
-	if (!try_module_get(dev->ib_dev->owner)) {
-		ret = -ENODEV;
+	srcu_key = srcu_read_lock(&dev->disassociate_srcu);
+	mutex_lock(&dev->lists_mutex);
+	ib_dev = srcu_dereference(dev->ib_dev,
+				  &dev->disassociate_srcu);
+	if (!ib_dev) {
+		ret = -EIO;
 		goto err;
 	}
 
-	file = kmalloc(sizeof *file, GFP_KERNEL);
+	/* In case IB device supports disassociate ucontext, there is no hard
+	 * dependency between uverbs device and its low level device.
+	 */
+	module_dependent = !(ib_dev->disassociate_ucontext);
+
+	if (module_dependent) {
+		if (!try_module_get(ib_dev->owner)) {
+			ret = -ENODEV;
+			goto err;
+		}
+	}
+
+	file = kzalloc(sizeof(*file), GFP_KERNEL);
 	if (!file) {
 		ret = -ENOMEM;
-		goto err_module;
+		if (module_dependent)
+			goto err_module;
+
+		goto err;
 	}
 
 	file->device	 = dev;
@@ -807,22 +920,38 @@ static int ib_uverbs_open(struct inode *inode, struct file *filp)
 	mutex_init(&file->mutex);
 
 	filp->private_data = file;
+	list_add_tail(&file->list, &dev->uverbs_file_list);
+	mutex_unlock(&dev->lists_mutex);
+	srcu_read_unlock(&dev->disassociate_srcu, srcu_key);
 
 	return nonseekable_open(inode, filp);
 
 err_module:
-	module_put(dev->ib_dev->owner);
+	module_put(ib_dev->owner);
 
 err:
-	kref_put(&dev->ref, ib_uverbs_release_dev);
+	mutex_unlock(&dev->lists_mutex);
+	srcu_read_unlock(&dev->disassociate_srcu, srcu_key);
+	kref_put(&dev->comp_ref, ib_uverbs_comp_dev);
+	kref_put(&dev->free_ref, ib_uverbs_release_dev);
 	return ret;
 }
 
 static int ib_uverbs_close(struct inode *inode, struct file *filp)
 {
 	struct ib_uverbs_file *file = filp->private_data;
-
-	ib_uverbs_cleanup_ucontext(file, file->ucontext);
+	struct ib_ucontext *ucontext = NULL;
+
+	mutex_lock(&file->device->lists_mutex);
+	ucontext = file->ucontext;
+	file->ucontext = NULL;
+	if (!file->is_closed) {
+		list_del(&file->list);
+		file->is_closed = 1;
+	}
+	mutex_unlock(&file->device->lists_mutex);
+	if (ucontext)
+		ib_uverbs_cleanup_ucontext(file, ucontext);
 
 	if (file->async_file)
 		kref_put(&file->async_file->ref, ib_uverbs_release_event_file);
@@ -858,12 +987,21 @@ static struct ib_client uverbs_client = {
 static ssize_t show_ibdev(struct device *device, struct device_attribute *attr,
 			  char *buf)
 {
+	int ret = -ENODEV;
+	int srcu_key;
 	struct ib_uverbs_device *dev = dev_get_drvdata(device);
+	struct ib_device *ib_dev;
 
 	if (!dev)
 		return -ENODEV;
 
-	return sprintf(buf, "%s\n", dev->ib_dev->name);
+	srcu_key = srcu_read_lock(&dev->disassociate_srcu);
+	ib_dev = srcu_dereference(dev->ib_dev, &dev->disassociate_srcu);
+	if (ib_dev)
+		ret = sprintf(buf, "%s\n", ib_dev->name);
+	srcu_read_unlock(&dev->disassociate_srcu, srcu_key);
+
+	return ret;
 }
 static DEVICE_ATTR(ibdev, S_IRUGO, show_ibdev, NULL);
 
@@ -871,11 +1009,19 @@ static ssize_t show_dev_abi_version(struct device *device,
 				    struct device_attribute *attr, char *buf)
 {
 	struct ib_uverbs_device *dev = dev_get_drvdata(device);
+	int ret = -ENODEV;
+	int srcu_key;
+	struct ib_device *ib_dev;
 
 	if (!dev)
 		return -ENODEV;
+	srcu_key = srcu_read_lock(&dev->disassociate_srcu);
+	ib_dev = srcu_dereference(dev->ib_dev, &dev->disassociate_srcu);
+	if (ib_dev)
+		ret = sprintf(buf, "%d\n", ib_dev->uverbs_abi_ver);
+	srcu_read_unlock(&dev->disassociate_srcu, srcu_key);
 
-	return sprintf(buf, "%d\n", dev->ib_dev->uverbs_abi_ver);
+	return ret;
 }
 static DEVICE_ATTR(abi_version, S_IRUGO, show_dev_abi_version, NULL);
 
@@ -915,6 +1061,7 @@ static void ib_uverbs_add_one(struct ib_device *device)
 	int devnum;
 	dev_t base;
 	struct ib_uverbs_device *uverbs_dev;
+	int ret;
 
 	if (!device->alloc_ucontext)
 		return;
@@ -923,10 +1070,20 @@ static void ib_uverbs_add_one(struct ib_device *device)
 	if (!uverbs_dev)
 		return;
 
-	kref_init(&uverbs_dev->ref);
+	ret = init_srcu_struct(&uverbs_dev->disassociate_srcu);
+	if (ret) {
+		kfree(uverbs_dev);
+		return;
+	}
+
+	kref_init(&uverbs_dev->comp_ref);
+	kref_init(&uverbs_dev->free_ref);
 	init_completion(&uverbs_dev->comp);
 	uverbs_dev->xrcd_tree = RB_ROOT;
 	mutex_init(&uverbs_dev->xrcd_tree_mutex);
+	mutex_init(&uverbs_dev->lists_mutex);
+	INIT_LIST_HEAD(&uverbs_dev->uverbs_file_list);
+	INIT_LIST_HEAD(&uverbs_dev->uverbs_events_file_list);
 
 	spin_lock(&map_lock);
 	devnum = find_first_zero_bit(dev_map, IB_UVERBS_MAX_DEVICES);
@@ -947,7 +1104,7 @@ static void ib_uverbs_add_one(struct ib_device *device)
 	}
 	spin_unlock(&map_lock);
 
-	uverbs_dev->ib_dev           = device;
+	rcu_assign_pointer(uverbs_dev->ib_dev, device);
 	uverbs_dev->num_comp_vectors = device->num_comp_vectors;
 
 	cdev_init(&uverbs_dev->cdev, NULL);
@@ -983,15 +1140,78 @@ err_cdev:
 		clear_bit(devnum, overflow_map);
 
 err:
-	kref_put(&uverbs_dev->ref, ib_uverbs_release_dev);
+	kref_put(&uverbs_dev->comp_ref, ib_uverbs_comp_dev);
 	wait_for_completion(&uverbs_dev->comp);
-	kfree(uverbs_dev);
+	kref_put(&uverbs_dev->free_ref, ib_uverbs_release_dev);
 	return;
 }
 
+static void ib_uverbs_free_hw_resources(struct ib_uverbs_device *uverbs_dev,
+					struct ib_device *ib_dev)
+{
+	struct ib_uverbs_file *file;
+	struct ib_uverbs_event_file *event_file;
+	struct ib_event event;
+
+	/* Pending running commands to terminate */
+	synchronize_srcu(&uverbs_dev->disassociate_srcu);
+	event.event = IB_EVENT_DEVICE_FATAL;
+	event.element.port_num = 0;
+	event.device = ib_dev;
+
+	mutex_lock(&uverbs_dev->lists_mutex);
+	while (!list_empty(&uverbs_dev->uverbs_file_list)) {
+		struct ib_ucontext *ucontext;
+
+		file = list_first_entry(&uverbs_dev->uverbs_file_list,
+					struct ib_uverbs_file, list);
+		file->is_closed = 1;
+		ucontext = file->ucontext;
+		list_del(&file->list);
+		file->ucontext = NULL;
+		kref_get(&file->ref);
+		mutex_unlock(&uverbs_dev->lists_mutex);
+		/* We must release the mutex before going ahead and calling
+		 * disassociate_ucontext. disassociate_ucontext might end up
+		 * indirectly calling uverbs_close, for example due to freeing
+		 * the resources (e.g mmput).
+		 */
+		ib_uverbs_event_handler(&file->event_handler, &event);
+		if (ucontext) {
+			ib_dev->disassociate_ucontext(ucontext);
+			ib_uverbs_cleanup_ucontext(file, ucontext);
+		}
+
+		mutex_lock(&uverbs_dev->lists_mutex);
+		kref_put(&file->ref, ib_uverbs_release_file);
+	}
+
+	while (!list_empty(&uverbs_dev->uverbs_events_file_list)) {
+		event_file = list_first_entry(&uverbs_dev->
+					      uverbs_events_file_list,
+					      struct ib_uverbs_event_file,
+					      list);
+		spin_lock_irq(&event_file->lock);
+		event_file->is_closed = 1;
+		spin_unlock_irq(&event_file->lock);
+
+		list_del(&event_file->list);
+		if (event_file->is_async) {
+			ib_unregister_event_handler(&event_file->uverbs_file->
+						    event_handler);
+			event_file->uverbs_file->event_handler.device = NULL;
+		}
+
+		wake_up_interruptible(&event_file->poll_wait);
+		kill_fasync(&event_file->async_queue, SIGIO, POLL_IN);
+	}
+	mutex_unlock(&uverbs_dev->lists_mutex);
+}
+
 static void ib_uverbs_remove_one(struct ib_device *device)
 {
 	struct ib_uverbs_device *uverbs_dev = ib_get_client_data(device, &uverbs_client);
+	int wait_clients = 1;
 
 	if (!uverbs_dev)
 		return;
@@ -1005,9 +1225,28 @@ static void ib_uverbs_remove_one(struct ib_device *device)
 	else
 		clear_bit(uverbs_dev->devnum - IB_UVERBS_MAX_DEVICES, overflow_map);
 
-	kref_put(&uverbs_dev->ref, ib_uverbs_release_dev);
-	wait_for_completion(&uverbs_dev->comp);
-	kfree(uverbs_dev);
+	if (device->disassociate_ucontext) {
+		/* We disassociate HW resources and immediately return.
+		 * Userspace will see a EIO errno for all future access.
+		 * Upon returning, ib_device may be freed internally and is not
+		 * valid any more.
+		 * uverbs_device is still available until all clients close
+		 * their files, then the uverbs device ref count will be zero
+		 * and its resources will be freed.
+		 * Note: At this point no more files can be opened since the
+		 * cdev was deleted, however active clients can still issue
+		 * commands and close their open files.
+		 */
+		rcu_assign_pointer(uverbs_dev->ib_dev, NULL);
+		ib_uverbs_free_hw_resources(uverbs_dev, device);
+		wait_clients = 0;
+	}
+
+	kref_put(&uverbs_dev->comp_ref, ib_uverbs_comp_dev);
+	if (wait_clients)
+		wait_for_completion(&uverbs_dev->comp);
+
+	kref_put(&uverbs_dev->free_ref, ib_uverbs_release_dev);
 }
 
 static char *uverbs_devnode(struct device *dev, umode_t *mode)
diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
index 986fddb..e30552f 100644
--- a/include/rdma/ib_verbs.h
+++ b/include/rdma/ib_verbs.h
@@ -1724,6 +1724,7 @@ struct ib_device {
 	int			   (*destroy_flow)(struct ib_flow *flow_id);
 	int			   (*check_mr_status)(struct ib_mr *mr, u32 check_mask,
 						      struct ib_mr_status *mr_status);
+	void			   (*disassociate_ucontext)(struct ib_ucontext *ibcontext);
 
 	struct ib_dma_mapping_ops   *dma_ops;
 
-- 
1.7.1

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Re: [PATCH for-next V6 3/5] IB/uverbs: Enable device removal when there are active user space applications

[Jason Gunthorpe]

On Tue, Jun 30, 2015 at 01:26:05PM +0300, Yishai Hadas wrote:
>  struct ib_uverbs_device {
> -	struct kref				ref;
> +	struct kref				comp_ref;
> +	struct kref				free_ref;

So.. I was looking at this, and there is something wrong with the
existing code. 

This old code:

	cdev_del(&uverbs_dev->cdev);
	[..]
 	wait_for_completion(&uverbs_dev->comp);
-	kfree(uverbs_dev);

Has built in to it an assumption that when cdev_del returns there can
be no possible open() running. Which doesn't appear to be true, cdev
calls open unlocked and relies on refcounting to make everything work
out.

Even other places in the rdma core work this way, eg user_mad.

Which means open can be running concurrently with the rest of that
stuff, which creates several obvious problems.

I *think* (and I am not totally sure) that when you use cdev with a
dynamic structure, it *must* be chained off of a kobject for the
containing structure. Certainly, other examples in the kernel I've
looked at recently do this. (Typically the cdev will be part of the

Ie it should look like this:

  struct ib_uverbs_device {
	struct kobject			        kobj;
	struct cdev			        cdev;

	cdev_init(&uverbs_dev->cdev, NULL);
	uverbs_dev->cdev.kobj.parent = &uverbs_dev->kobj;
	cdev_add(..)

The cdev will hold a kref on the parent (the containing structure) and
only when that kref is released is it guaranteed that open will never
be called again.

So, kobj becomes your free_ref, and cdev properly chains off it to
close that little hole with kref.

---

The next problem is that open can run concurrently with
wait_for_completion, so the waiting scheme is wrong too.

This is a great example of why you should never use a kref for an
active count. It seems like the right thing, but it is subtly wrong.

krefs have this special property:

kref_get()
        WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2);

So when the code did this:

-	kref_put(&uverbs_dev->ref, ib_uverbs_release_dev);
-	wait_for_completion(&uverbs_dev->comp);
-	kfree(uverbs_dev);

There is a race where another CPU may be in ib_uverbs_open
about to do kref_get, which will trigger the above WARN_ON, or a
use after free race with the kfree

A good way to implement this pattern is to use an atomic with a
bias. See how kernfs_get_active/kernfs_put_active/kernfs_drain work
for a very good example of this scheme.

This is an existing bug, I think a dedicated patch which
 - adds the kobj and moves the kfree(uverbs_dev) into it
 - Fixes the active count scheme to use an atomic not a kref

Would be appropriate. Once done the disassociate patch doesn't have to
really do anything with this stuff.

I would also recommend looking at other uses of cdev_add in the rdma
core, they may be similarly off..

Jason
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Re: [PATCH for-next V6 3/5] IB/uverbs: Enable device removal when there are active user space applications

[Yishai Hadas]

On 6/30/2015 9:40 PM, Jason Gunthorpe wrote:
> On Tue, Jun 30, 2015 at 01:26:05PM +0300, Yishai Hadas wrote:
>>   struct ib_uverbs_device {
>> -	struct kref				ref;
>> +	struct kref				comp_ref;
>> +	struct kref				free_ref;
>
> So.. I was looking at this, and there is something wrong with the
> existing code.
>
> This old code:
>
> 	cdev_del(&uverbs_dev->cdev);
> 	[..]
>   	wait_for_completion(&uverbs_dev->comp);
> -	kfree(uverbs_dev);
>
> Has built in to it an assumption that when cdev_del returns there can
> be no possible open() running. Which doesn't appear to be true, cdev
> calls open unlocked and relies on refcounting to make everything work
> out.

The patch that introduces this bug was added 5 years ago by Alex Chiang 
and Signed-off-by: Roland Dreier.

Look at commit ID:2a72f212263701b927559f6850446421d5906c41, it can be 
seen also at: 
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=2a72f212263701b 


Before this commit there was a device look-up table that was protected 
by a spin_lock used by ib_uverbs_open and by ib_uverbs_remove_one. When 
it was dropped and container_of was used instead, it enabled the race 
with remove_one as dev might be freed just after:
dev = container_of(inode->i_cdev, struct ib_uverbs_device, cdev) but 
before the kref_get.

In addition, this buggy patch added some dead code as 
container_of(x,y,z) can never be NULL and so dev can never be NULL.
As a result the comment above ib_uverbs_open saying "the open method 
will either immediately run -ENXIO" is wrong as it can never happen.

  static int ib_uverbs_open(struct inode *inode, struct file *filp)
  {
@@ -631,13 +628,10 @@ static int ib_uverbs_open(struct inode *inode, 
struct file *filp)
  	struct ib_uverbs_file *file;
  	int ret;

-	spin_lock(&map_lock);
-	dev = dev_table[iminor(inode) - IB_UVERBS_BASE_MINOR];
+	dev = container_of(inode->i_cdev, struct ib_uverbs_device, cdev);
  	if (dev)
  		kref_get(&dev->ref);
-	spin_unlock(&map_lock);
-
-	if (!dev)
+	else
  		return -ENXIO;


Doug/Jason,
AFAIK V6 addressed all opened comments raised by Jason, including the 
last one that asked to use 2 separate krefs for both complete and free, 
it didn't introduced the problem above.

I believe that we should go forward and take the series. Please consider 
that this series fixes an existing oops in patch #1 and adds a missing 
functionality in the kernel, "Enable device removal when there are 
active user space clients".

To fix the existing 5 years bug an orthogonal patch that fixes the buggy 
patch should be sent.

Alex/Roland:
Please review above, any option that you'll contribute a patch that 
solves that problem ? any comment on ?



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Re: [PATCH for-next V6 3/5] IB/uverbs: Enable device removal when there are active user space applications

[Jason Gunthorpe]

On Mon, Jul 06, 2015 at 05:08:08PM +0300, Yishai Hadas wrote:

> The patch that introduces this bug was added 5 years ago by Alex Chiang and
> Signed-off-by: Roland Dreier.
> 
> Look at commit ID:2a72f212263701b927559f6850446421d5906c41, it can be seen
> also at:
> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=2a72f212263701b

Perhaps, this one also looks involved as well:

commit 055422ddbb0a7610c5f57a056743d7336a39e90f
Author: Alexander Chiang <achiang-VXdhtT5mjnY@public.gmane.org>
Date:   Tue Feb 2 19:07:49 2010 +0000

    IB/uverbs: Convert *cdev to cdev in struct ib_uverbs_device
    
    Instead of storing a pointer to a cdev, embed the entire struct cdev.

Embedding the cdev without using a parent kobject looks like the root
mistake.

> AFAIK V6 addressed all opened comments raised by Jason, including the last
> one that asked to use 2 separate krefs for both complete and free, it didn't
> introduced the problem above.

It does make it worse though, previously the module locking would make
it unlikely to ever hit any problem here, but now we have a naked
fully exposed race where release races with kfree resulting in
use-after-free. I'd think hitting it is quite likely if the new
feature is being used, and subtle memory corruption is not something
we want to see in the kernel.

So, I'd say, yes it is an old bug, but it is unlikely to hit it. This
patch series is making it much likely, so it needs to be fixed.

In any event, I'm not sure what you are complaining about - this
series absolutely reworks the lifetime model of ib_uverbs_device, why
on earth do you think it is OK to have a buggy new implementation just
because the previous version was buggy? *Especially* when someone
takes the time to point out the mistake and tells you exactly how to
fix it, and it is *trival* to do?

Even worse: I went through and audited the lifetime of V6's new model,
and I think that is *absolutely* something you should have done before
sending V1 :(

Jason
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[PATCH for-next V6 4/5] IB/mlx4_ib: Disassociate support

[Yishai Hadas]

Implements the IB core disassociate_ucontext API. The driver detaches the HW
resources for a given user context to prevent a dependency between application
termination and device disconnecting. This is done by managing the VMAs that
were mapped to the HW bars such as door bell and blueflame. When need to detach
remap them to an arbitrary kernel page returned by the zap API.

Signed-off-by: Yishai Hadas <yishaih-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Signed-off-by: Jack Morgenstein <jackm-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
---
 drivers/infiniband/hw/mlx4/main.c    |  139 +++++++++++++++++++++++++++++++++-
 drivers/infiniband/hw/mlx4/mlx4_ib.h |   13 +++
 2 files changed, 150 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/hw/mlx4/main.c b/drivers/infiniband/hw/mlx4/main.c
index 166da78..456c60c 100644
--- a/drivers/infiniband/hw/mlx4/main.c
+++ b/drivers/infiniband/hw/mlx4/main.c
@@ -691,7 +691,7 @@ static struct ib_ucontext *mlx4_ib_alloc_ucontext(struct ib_device *ibdev,
 		resp.cqe_size	      = dev->dev->caps.cqe_size;
 	}
 
-	context = kmalloc(sizeof *context, GFP_KERNEL);
+	context = kzalloc(sizeof(*context), GFP_KERNEL);
 	if (!context)
 		return ERR_PTR(-ENOMEM);
 
@@ -728,21 +728,143 @@ static int mlx4_ib_dealloc_ucontext(struct ib_ucontext *ibcontext)
 	return 0;
 }
 
+static void  mlx4_ib_vma_open(struct vm_area_struct *area)
+{
+	/* vma_open is called when a new VMA is created on top of our VMA.
+	 * This is done through either mremap flow or split_vma (usually due
+	 * to mlock, madvise, munmap, etc.). We do not support a clone of the
+	 * vma, as this VMA is strongly hardware related. Therefore we set the
+	 * vm_ops of the newly created/cloned VMA to NULL, to prevent it from
+	 * calling us again and trying to do incorrect actions. We assume that
+	 * the original vma size is exactly a single page that there will be no
+	 * "splitting" operations on.
+	 */
+	area->vm_ops = NULL;
+}
+
+static void  mlx4_ib_vma_close(struct vm_area_struct *area)
+{
+	struct mlx4_ib_vma_private_data *mlx4_ib_vma_priv_data;
+
+	/* It's guaranteed that all VMAs opened on a FD are closed before the
+	 * file itself is closed, therefore no sync is needed with the regular
+	 * closing flow. (e.g. mlx4_ib_dealloc_ucontext) However need a sync
+	 * with accessing the vma as part of mlx4_ib_disassociate_ucontext.
+	 * The close operation is usually called under mm->mmap_sem except when
+	 * process is exiting.  The exiting case is handled explicitly as part
+	 * of mlx4_ib_disassociate_ucontext.
+	 */
+	mlx4_ib_vma_priv_data = (struct mlx4_ib_vma_private_data *)
+				area->vm_private_data;
+
+	/* set the vma context pointer to null in the mlx4_ib driver's private
+	 * data to protect against a race condition in mlx4_ib_dissassociate_ucontext().
+	 */
+	mlx4_ib_vma_priv_data->vma = NULL;
+}
+
+static const struct vm_operations_struct mlx4_ib_vm_ops = {
+	.open = mlx4_ib_vma_open,
+	.close = mlx4_ib_vma_close
+};
+
+static void mlx4_ib_disassociate_ucontext(struct ib_ucontext *ibcontext)
+{
+	int i;
+	int ret = 0;
+	struct vm_area_struct *vma;
+	struct mlx4_ib_ucontext *context = to_mucontext(ibcontext);
+	struct task_struct *owning_process  = NULL;
+	struct mm_struct   *owning_mm       = NULL;
+
+	owning_process = get_pid_task(ibcontext->tgid, PIDTYPE_PID);
+	if (!owning_process)
+		return;
+
+	owning_mm = get_task_mm(owning_process);
+	if (!owning_mm) {
+		pr_info("no mm, disassociate ucontext is pending task termination\n");
+		while (1) {
+			/* make sure that task is dead before returning, it may
+			 * prevent a rare case of module down in parallel to a
+			 * call to mlx4_ib_vma_close.
+			 */
+			put_task_struct(owning_process);
+			msleep(1);
+			owning_process = get_pid_task(ibcontext->tgid,
+						      PIDTYPE_PID);
+			if (!owning_process ||
+			    owning_process->state == TASK_DEAD) {
+				pr_info("disassociate ucontext done, task was terminated\n");
+				/* in case task was dead need to release the task struct */
+				if (owning_process)
+					put_task_struct(owning_process);
+				return;
+			}
+		}
+	}
+
+	/* need to protect from a race on closing the vma as part of
+	 * mlx4_ib_vma_close().
+	 */
+	down_read(&owning_mm->mmap_sem);
+	for (i = 0; i < HW_BAR_COUNT; i++) {
+		vma = context->hw_bar_info[i].vma;
+		if (!vma)
+			continue;
+
+		ret = zap_vma_ptes(context->hw_bar_info[i].vma,
+				   context->hw_bar_info[i].vma->vm_start,
+				   PAGE_SIZE);
+		if (ret) {
+			pr_err("Error: zap_vma_ptes failed for index=%d, ret=%d\n", i, ret);
+			BUG_ON(1);
+		}
+
+		/* context going to be destroyed, should not access ops any more */
+		context->hw_bar_info[i].vma->vm_ops = NULL;
+	}
+
+	up_read(&owning_mm->mmap_sem);
+	mmput(owning_mm);
+	put_task_struct(owning_process);
+}
+
+static void mlx4_ib_set_vma_data(struct vm_area_struct *vma,
+				 struct mlx4_ib_vma_private_data *vma_private_data)
+{
+	vma_private_data->vma = vma;
+	vma->vm_private_data = vma_private_data;
+	vma->vm_ops =  &mlx4_ib_vm_ops;
+}
+
 static int mlx4_ib_mmap(struct ib_ucontext *context, struct vm_area_struct *vma)
 {
 	struct mlx4_ib_dev *dev = to_mdev(context->device);
+	struct mlx4_ib_ucontext *mucontext = to_mucontext(context);
 
 	if (vma->vm_end - vma->vm_start != PAGE_SIZE)
 		return -EINVAL;
 
 	if (vma->vm_pgoff == 0) {
+		/* We prevent double mmaping on same context */
+		if (mucontext->hw_bar_info[HW_BAR_DB].vma)
+			return -EINVAL;
+
 		vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
 
 		if (io_remap_pfn_range(vma, vma->vm_start,
 				       to_mucontext(context)->uar.pfn,
 				       PAGE_SIZE, vma->vm_page_prot))
 			return -EAGAIN;
+
+		mlx4_ib_set_vma_data(vma, &mucontext->hw_bar_info[HW_BAR_DB]);
+
 	} else if (vma->vm_pgoff == 1 && dev->dev->caps.bf_reg_size != 0) {
+		/* We prevent double mmaping on same context */
+		if (mucontext->hw_bar_info[HW_BAR_BF].vma)
+			return -EINVAL;
+
 		vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
 
 		if (io_remap_pfn_range(vma, vma->vm_start,
@@ -750,9 +872,18 @@ static int mlx4_ib_mmap(struct ib_ucontext *context, struct vm_area_struct *vma)
 				       dev->dev->caps.num_uars,
 				       PAGE_SIZE, vma->vm_page_prot))
 			return -EAGAIN;
+
+		mlx4_ib_set_vma_data(vma, &mucontext->hw_bar_info[HW_BAR_BF]);
+
 	} else if (vma->vm_pgoff == 3) {
 		struct mlx4_clock_params params;
-		int ret = mlx4_get_internal_clock_params(dev->dev, &params);
+		int ret;
+
+		/* We prevent double mmaping on same context */
+		if (mucontext->hw_bar_info[HW_BAR_CLOCK].vma)
+			return -EINVAL;
+
+		ret = mlx4_get_internal_clock_params(dev->dev, &params);
 
 		if (ret)
 			return ret;
@@ -765,6 +896,9 @@ static int mlx4_ib_mmap(struct ib_ucontext *context, struct vm_area_struct *vma)
 				       >> PAGE_SHIFT,
 				       PAGE_SIZE, vma->vm_page_prot))
 			return -EAGAIN;
+
+		mlx4_ib_set_vma_data(vma,
+				     &mucontext->hw_bar_info[HW_BAR_CLOCK]);
 	} else {
 		return -EINVAL;
 	}
@@ -2322,6 +2456,7 @@ static void *mlx4_ib_add(struct mlx4_dev *dev)
 	ibdev->ib_dev.detach_mcast	= mlx4_ib_mcg_detach;
 	ibdev->ib_dev.process_mad	= mlx4_ib_process_mad;
 	ibdev->ib_dev.get_port_immutable = mlx4_port_immutable;
+	ibdev->ib_dev.disassociate_ucontext = mlx4_ib_disassociate_ucontext;
 
 	if (!mlx4_is_slave(ibdev->dev)) {
 		ibdev->ib_dev.alloc_fmr		= mlx4_ib_fmr_alloc;
diff --git a/drivers/infiniband/hw/mlx4/mlx4_ib.h b/drivers/infiniband/hw/mlx4/mlx4_ib.h
index 7933adf..4d7f6ed 100644
--- a/drivers/infiniband/hw/mlx4/mlx4_ib.h
+++ b/drivers/infiniband/hw/mlx4/mlx4_ib.h
@@ -70,11 +70,24 @@ extern int mlx4_ib_sm_guid_assign;
 
 #define MLX4_IB_UC_STEER_QPN_ALIGN 1
 #define MLX4_IB_UC_MAX_NUM_QPS     256
+
+enum hw_bar_type {
+	HW_BAR_BF,
+	HW_BAR_DB,
+	HW_BAR_CLOCK,
+	HW_BAR_COUNT
+};
+
+struct mlx4_ib_vma_private_data {
+	struct vm_area_struct *vma;
+};
+
 struct mlx4_ib_ucontext {
 	struct ib_ucontext	ibucontext;
 	struct mlx4_uar		uar;
 	struct list_head	db_page_list;
 	struct mutex		db_page_mutex;
+	struct mlx4_ib_vma_private_data hw_bar_info[HW_BAR_COUNT];
 };
 
 struct mlx4_ib_pd {
-- 
1.7.1

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[PATCH for-next V6 5/5] IB/ucma: HW Device hot-removal support

[Yishai Hadas]

Currently, IB/cma remove_one flow blocks until all user descriptor managed by
IB/ucma are released. This prevents hot-removal of IB devices. This patch
allows IB/cma to remove devices regardless of user space activity. Upon getting
the RDMA_CM_EVENT_DEVICE_REMOVAL event we close all the underlying HW resources
for the given ucontext. The ucontext itself is still alive till its explicit
destroying by its creator.

Running applications at that time will have some zombie device, further
operations may fail.

Signed-off-by: Yishai Hadas <yishaih-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Signed-off-by: Shachar Raindel <raindel-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
---
 drivers/infiniband/core/ucma.c |  130 ++++++++++++++++++++++++++++++++++++----
 1 files changed, 119 insertions(+), 11 deletions(-)

diff --git a/drivers/infiniband/core/ucma.c b/drivers/infiniband/core/ucma.c
index ad45469..e35990f 100644
--- a/drivers/infiniband/core/ucma.c
+++ b/drivers/infiniband/core/ucma.c
@@ -74,6 +74,7 @@ struct ucma_file {
 	struct list_head	ctx_list;
 	struct list_head	event_list;
 	wait_queue_head_t	poll_wait;
+	struct workqueue_struct	*close_wq;
 };
 
 struct ucma_context {
@@ -89,6 +90,9 @@ struct ucma_context {
 
 	struct list_head	list;
 	struct list_head	mc_list;
+	int			closing;
+	int			destroying;
+	struct work_struct	close_work;
 };
 
 struct ucma_multicast {
@@ -107,6 +111,7 @@ struct ucma_event {
 	struct list_head	list;
 	struct rdma_cm_id	*cm_id;
 	struct rdma_ucm_event_resp resp;
+	struct work_struct	close_work;
 };
 
 static DEFINE_MUTEX(mut);
@@ -132,8 +137,12 @@ static struct ucma_context *ucma_get_ctx(struct ucma_file *file, int id)
 
 	mutex_lock(&mut);
 	ctx = _ucma_find_context(id, file);
-	if (!IS_ERR(ctx))
-		atomic_inc(&ctx->ref);
+	if (!IS_ERR(ctx)) {
+		if (ctx->closing)
+			ctx = ERR_PTR(-EIO);
+		else
+			atomic_inc(&ctx->ref);
+	}
 	mutex_unlock(&mut);
 	return ctx;
 }
@@ -144,6 +153,34 @@ static void ucma_put_ctx(struct ucma_context *ctx)
 		complete(&ctx->comp);
 }
 
+static void ucma_close_event_id(struct work_struct *work)
+{
+	struct ucma_event *uevent_close =  container_of(work, struct ucma_event, close_work);
+
+	rdma_destroy_id(uevent_close->cm_id);
+	kfree(uevent_close);
+}
+
+static void ucma_close_id(struct work_struct *work)
+{
+	struct ucma_context *ctx =  container_of(work, struct ucma_context, close_work);
+
+	/* Fence to ensure that ctx->closing was seen by all
+	 * ucma_get_ctx running
+	 */
+	mutex_lock(&mut);
+	mutex_unlock(&mut);
+
+	/* once all inflight tasks are finished, we close all underlying
+	 * resources. The context is still alive till its explicit destryoing
+	 * by its creator.
+	 */
+	ucma_put_ctx(ctx);
+	wait_for_completion(&ctx->comp);
+	/* No new events will be generated after destroying the id. */
+	rdma_destroy_id(ctx->cm_id);
+}
+
 static struct ucma_context *ucma_alloc_ctx(struct ucma_file *file)
 {
 	struct ucma_context *ctx;
@@ -152,6 +189,7 @@ static struct ucma_context *ucma_alloc_ctx(struct ucma_file *file)
 	if (!ctx)
 		return NULL;
 
+	INIT_WORK(&ctx->close_work, ucma_close_id);
 	atomic_set(&ctx->ref, 1);
 	init_completion(&ctx->comp);
 	INIT_LIST_HEAD(&ctx->mc_list);
@@ -242,6 +280,42 @@ static void ucma_set_event_context(struct ucma_context *ctx,
 	}
 }
 
+/* Called with file->mut locked for the relevant context. */
+static void ucma_removal_event_handler(struct rdma_cm_id *cm_id)
+{
+	struct ucma_context *ctx = cm_id->context;
+	struct ucma_event *con_req_eve;
+	int event_found = 0;
+
+	if (ctx->destroying)
+		return;
+
+	/* only if context is pointing to cm_id that it owns it and can be
+	 * queued to be closed, otherwise that cm_id is an inflight one that
+	 * is part of that context event list pending to be detached and
+	 * reattached to its new context as part of ucma_get_event,
+	 * handled separately below.
+	 */
+	if (ctx->cm_id == cm_id) {
+		ctx->closing = 1;
+		queue_work(ctx->file->close_wq, &ctx->close_work);
+		return;
+	}
+
+	list_for_each_entry(con_req_eve, &ctx->file->event_list, list) {
+		if (con_req_eve->cm_id == cm_id &&
+		    con_req_eve->resp.event == RDMA_CM_EVENT_CONNECT_REQUEST) {
+			list_del(&con_req_eve->list);
+			INIT_WORK(&con_req_eve->close_work, ucma_close_event_id);
+			queue_work(ctx->file->close_wq, &con_req_eve->close_work);
+			event_found = 1;
+			break;
+		}
+	}
+	if (!event_found)
+		printk(KERN_ERR "ucma_removal_event_handler: warning: connect request event wasn't found\n");
+}
+
 static int ucma_event_handler(struct rdma_cm_id *cm_id,
 			      struct rdma_cm_event *event)
 {
@@ -276,14 +350,21 @@ static int ucma_event_handler(struct rdma_cm_id *cm_id,
 		 * We ignore events for new connections until userspace has set
 		 * their context.  This can only happen if an error occurs on a
 		 * new connection before the user accepts it.  This is okay,
-		 * since the accept will just fail later.
+		 * since the accept will just fail later. However, we do need
+		 * to release the underlying HW resources in case of a device
+		 * removal event.
 		 */
+		if (event->event == RDMA_CM_EVENT_DEVICE_REMOVAL)
+			ucma_removal_event_handler(cm_id);
+
 		kfree(uevent);
 		goto out;
 	}
 
 	list_add_tail(&uevent->list, &ctx->file->event_list);
 	wake_up_interruptible(&ctx->file->poll_wait);
+	if (event->event == RDMA_CM_EVENT_DEVICE_REMOVAL)
+		ucma_removal_event_handler(cm_id);
 out:
 	mutex_unlock(&ctx->file->mut);
 	return ret;
@@ -442,9 +523,15 @@ static void ucma_cleanup_mc_events(struct ucma_multicast *mc)
 }
 
 /*
- * We cannot hold file->mut when calling rdma_destroy_id() or we can
- * deadlock.  We also acquire file->mut in ucma_event_handler(), and
- * rdma_destroy_id() will wait until all callbacks have completed.
+ * ucma_free_ctx is called after the underlying rdma CM-ID is destroyed. At
+ * this point, no new events will be reported from the hardware. However, we
+ * still need to cleanup the UCMA context for this ID. Specifically, there
+ * might be events that have not yet been consumed by the user space software.
+ * These might include pending connect requests which we have not completed
+ * processing.  We cannot call rdma_destroy_id while holding the lock of the
+ * context (file->mut), as it might cause a deadlock. We therefore extract all
+ * relevant events from the context pending events list while holding the
+ * mutex. After that we release them as needed.
  */
 static int ucma_free_ctx(struct ucma_context *ctx)
 {
@@ -452,8 +539,6 @@ static int ucma_free_ctx(struct ucma_context *ctx)
 	struct ucma_event *uevent, *tmp;
 	LIST_HEAD(list);
 
-	/* No new events will be generated after destroying the id. */
-	rdma_destroy_id(ctx->cm_id);
 
 	ucma_cleanup_multicast(ctx);
 
@@ -501,10 +586,20 @@ static ssize_t ucma_destroy_id(struct ucma_file *file, const char __user *inbuf,
 	if (IS_ERR(ctx))
 		return PTR_ERR(ctx);
 
-	ucma_put_ctx(ctx);
-	wait_for_completion(&ctx->comp);
-	resp.events_reported = ucma_free_ctx(ctx);
+	mutex_lock(&ctx->file->mut);
+	ctx->destroying = 1;
+	mutex_unlock(&ctx->file->mut);
+
+	flush_workqueue(ctx->file->close_wq);
+	/* At this point it's guaranteed that there is no inflight
+	 * closing task */
+	if (!ctx->closing) {
+		ucma_put_ctx(ctx);
+		wait_for_completion(&ctx->comp);
+		rdma_destroy_id(ctx->cm_id);
+	}
 
+	resp.events_reported = ucma_free_ctx(ctx);
 	if (copy_to_user((void __user *)(unsigned long)cmd.response,
 			 &resp, sizeof(resp)))
 		ret = -EFAULT;
@@ -1529,6 +1624,7 @@ static int ucma_open(struct inode *inode, struct file *filp)
 	INIT_LIST_HEAD(&file->ctx_list);
 	init_waitqueue_head(&file->poll_wait);
 	mutex_init(&file->mut);
+	file->close_wq = create_singlethread_workqueue("ucma_close_id");
 
 	filp->private_data = file;
 	file->filp = filp;
@@ -1543,16 +1639,28 @@ static int ucma_close(struct inode *inode, struct file *filp)
 
 	mutex_lock(&file->mut);
 	list_for_each_entry_safe(ctx, tmp, &file->ctx_list, list) {
+		ctx->destroying = 1;
 		mutex_unlock(&file->mut);
 
 		mutex_lock(&mut);
 		idr_remove(&ctx_idr, ctx->id);
 		mutex_unlock(&mut);
 
+		flush_workqueue(file->close_wq);
+		/* At that step once ctx was marked as destroying and workqueue
+		 * was flushed we are safe from any inflights handlers that
+		 * might put other closing task.
+		 */
+		if (!ctx->closing)
+			/* rdma_destroy_id ensures that no event handlers are
+			 * inflight for that id before releasing it.
+			 */
+			rdma_destroy_id(ctx->cm_id);
 		ucma_free_ctx(ctx);
 		mutex_lock(&file->mut);
 	}
 	mutex_unlock(&file->mut);
+	destroy_workqueue(file->close_wq);
 	kfree(file);
 	return 0;
 }
-- 
1.7.1

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Re: [PATCH for-next V6 0/5] HW Device hot-removal support

[Doug Ledford]

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On 06/30/2015 06:26 AM, Yishai Hadas wrote:
> Currently, if there is any user space application using an IB device,
> it is impossible to unload the HW device driver for this device.
> 
> Similarly, if the device is hot-unplugged or reset, the device driver
> hardware removal flow blocks until all user contexts are destroyed.
> 
> This patchset removes the above limitations from both uverbs and ucma.
> 
> The IB-core and uverbs layers are still required to remain loaded as
> long as there are user applications using the verbs API. However, the
> hardware device drivers are not blocked any more by the user space
> activity.
> 
> To support this, the hardware device needs to expose a new kernel API
> named 'disassociate_ucontext'. The device driver is given a ucontext
> to detach from, and it should block this user context from any future
> hardware access. In the IB-core level, we use this interface to
> deactivate all ucontext that address a specific device when handling a
> remove_one callback for it.
> 
> In the RDMA-CM layer, a similar change is needed in the ucma module,
> to prevent blocking of the remove_one operation. This allows for
> hot-removal of devices with RDMA-CM users in the user space.
> 
> The first two patches are preparation for this series.
> The first patch fixes a reference counting issue pointed by Jason Gunthorpe.
> The second patch is a preparation step for deploying RCU for the device
> removal flow.
> 
> The third patch introduces the new API between the HW device driver and
> the IB core. For devices which implement the functionality, IB core
> will use it in remove_one, disassociating any active ucontext from the
> hardware device. Other drivers that didn't implement it will behave as
> today, remove_one will block until all ucontexts referring the device
> are destroyed before returning.
> 
> The fourth patch provides implementation of this API for the mlx4
> driver.
> 
> The last patch extends ucma to avoid blocking remove_one operation in
> the cma module. When such device removal event is received, ucma is
> turning all user contexts to zombie contexts. This is done by
> releasing all underlying resources and preventing any further user
> operations on the context.
> 
> Changes from V5:
> Addressed Jason's comments for below patches:
> patch #1: Improve kref usage.
> patch #3: Use 2 different krefs for complete and memory, improve some comments.
> 
> Changes from V4:
> patch #1,#3 - addressed Jason's comments.
> patch #2, #4 - rebased upon last stuff.
> 
> Changes from V3:
> Add 2 patches as a preparation for this series, details above.
> patch #3: Change the locking schema based on Jason's comments.
> 
> Changes from V2:
> patch #1: Rebase over ODP patches.
> 
> Changes from V1:
> patch #1: Use uverbs flags instead of disassociate support, drop fatal_event_raised flag.
> patch #3: Add support in ucma for handling device removal.
> 
> Changes from V0:
> patch #1: ib_uverbs_close, reduced mutex scope to enable tasks run in parallel.
> Yishai Hadas (5):
>   IB/uverbs: Fix reference counting usage of event files
>   IB/uverbs: Explicitly pass ib_dev to uverbs commands
>   IB/uverbs: Enable device removal when there are active user space
>     applications
>   IB/mlx4_ib: Disassociate support
>   IB/ucma: HW Device hot-removal support
> 
>  drivers/infiniband/core/ucma.c        |  130 +++++++++-
>  drivers/infiniband/core/uverbs.h      |   16 +-
>  drivers/infiniband/core/uverbs_cmd.c  |  114 ++++++----
>  drivers/infiniband/core/uverbs_main.c |  438 +++++++++++++++++++++++++++------
>  drivers/infiniband/hw/mlx4/main.c     |  139 ++++++++++-
>  drivers/infiniband/hw/mlx4/mlx4_ib.h  |   13 +
>  include/rdma/ib_verbs.h               |    1 +
>  7 files changed, 714 insertions(+), 137 deletions(-)
> 

I've pulled this series in for 4.3.  There were some additional items in
some of Jason's comments that ought to be looked into, but I think this
patch set has reached the point where it's no worse than existing in
terms of locking, there were just some existing issues that should be
addressed too.

-- 
Doug Ledford <dledford-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
              GPG KeyID: 0E572FDD



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Re: [PATCH for-next V6 0/5] HW Device hot-removal support

[Jason Gunthorpe]

On Thu, Jul 30, 2015 at 12:46:52PM -0400, Doug Ledford wrote:

> I've pulled this series in for 4.3.  There were some additional items in
> some of Jason's comments that ought to be looked into, but I think this
> patch set has reached the point where it's no worse than existing in
> terms of locking, there were just some existing issues that should be
> addressed too.

Eh? V6 corrupts random kernel memory if you use the hot-removal.

Jason
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Re: [PATCH for-next V6 0/5] HW Device hot-removal support

[Doug Ledford]

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On 07/30/2015 12:50 PM, Jason Gunthorpe wrote:
> On Thu, Jul 30, 2015 at 12:46:52PM -0400, Doug Ledford wrote:
> 
>> I've pulled this series in for 4.3.  There were some additional items in
>> some of Jason's comments that ought to be looked into, but I think this
>> patch set has reached the point where it's no worse than existing in
>> terms of locking, there were just some existing issues that should be
>> addressed too.
> 
> Eh? V6 corrupts random kernel memory if you use the hot-removal.

I didn't see that in there.  Did I read through the discussion too fast?
 I'll go recheck...


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              GPG KeyID: 0E572FDD



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Re: [PATCH for-next V6 0/5] HW Device hot-removal support

[Jason Gunthorpe]

On Thu, Jul 30, 2015 at 12:59:30PM -0400, Doug Ledford wrote:
> On 07/30/2015 12:50 PM, Jason Gunthorpe wrote:
> > On Thu, Jul 30, 2015 at 12:46:52PM -0400, Doug Ledford wrote:
> > 
> >> I've pulled this series in for 4.3.  There were some additional items in
> >> some of Jason's comments that ought to be looked into, but I think this
> >> patch set has reached the point where it's no worse than existing in
> >> terms of locking, there were just some existing issues that should be
> >> addressed too.
> > 
> > Eh? V6 corrupts random kernel memory if you use the hot-removal.
> 
> I didn't see that in there.  Did I read through the discussion too fast?
>  I'll go recheck...

For a char device you absolutely cannot kfree the cdev in the file
release callback.

The file still holds a ref on cdev and it will guarenteed use
after-free on cdev during core code struct file cleanup.

Jason
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Re: [PATCH for-next V6 0/5] HW Device hot-removal support

[Doug Ledford]

[-- Attachment #1: Type: text/plain, Size: 1763 bytes --]

On 07/30/2015 01:09 PM, Jason Gunthorpe wrote:
> On Thu, Jul 30, 2015 at 12:59:30PM -0400, Doug Ledford wrote:
>> On 07/30/2015 12:50 PM, Jason Gunthorpe wrote:
>>> On Thu, Jul 30, 2015 at 12:46:52PM -0400, Doug Ledford wrote:
>>>
>>>> I've pulled this series in for 4.3.  There were some additional items in
>>>> some of Jason's comments that ought to be looked into, but I think this
>>>> patch set has reached the point where it's no worse than existing in
>>>> terms of locking, there were just some existing issues that should be
>>>> addressed too.
>>>
>>> Eh? V6 corrupts random kernel memory if you use the hot-removal.
>>
>> I didn't see that in there.  Did I read through the discussion too fast?
>>  I'll go recheck...
> 
> For a char device you absolutely cannot kfree the cdev in the file
> release callback.
> 
> The file still holds a ref on cdev and it will guarenteed use
> after-free on cdev during core code struct file cleanup.

OK, I see what happened.  The early discussion for patch 3/5 (the
problem patch) happened on list without me on Cc:, only the last few
messages had me on Cc:.  The net result is that I had seen yours and
Or's responses in my Inbox some weeks ago and that had leaked out of my
head, and what was in my linux-rdma folder didn't have those messages,
so when I read through this thread there, it was missing part of that
context.  When I re-read it via patchworks, all of the messages were in
one place.

Yishai, I currently have this code in my tree, but I'm going to cull it
and wait for a v7 that fixes this problem.  Please move that forward if
you want to make 4.3.


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