[PATCH 0/2] android: binder: resolve lru, dentry and task deadlock

[PATCH 0/2] android: binder: resolve lru, dentry and task deadlock

[Sherry Yang]

This patch set removes the unused vma argument in update_page_range
and resolves a potential deadlock between lru lock, task lock and
dentry lock reported by lockdep.

    android: binder: Don't get mm from task
    android: binder: Remove unused vma argument

drivers/android/binder_alloc.c | 36 ++++++-------
drivers/android/binder_alloc.h |  1 -
2 files changed, 15 insertions(+), 22 deletions(-)

[PATCH 1/2] android: binder: Remove unused vma argument

[Sherry Yang]

The vma argument in update_page_range is no longer
used after 74310e06 ("android: binder: Move buffer
out of area shared with user space"), since mmap_handler
no longer calls update_page_range with a vma.

Acked-by: Arve Hjønnevåg <arve@android.com>
Signed-off-by: Sherry Yang <sherryy@android.com>
---
 drivers/android/binder_alloc.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 064f5e31ec55..b87ecf77f9d1 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -186,12 +186,12 @@ struct binder_buffer *binder_alloc_prepare_to_free(struct binder_alloc *alloc,
 }
 
 static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
-				    void *start, void *end,
-				    struct vm_area_struct *vma)
+				    void *start, void *end)
 {
 	void *page_addr;
 	unsigned long user_page_addr;
 	struct binder_lru_page *page;
+	struct vm_area_struct *vma = NULL;
 	struct mm_struct *mm = NULL;
 	bool need_mm = false;
 
@@ -215,7 +215,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
 		}
 	}
 
-	if (!vma && need_mm)
+	if (need_mm)
 		mm = get_task_mm(alloc->tsk);
 
 	if (mm) {
@@ -442,7 +442,7 @@ struct binder_buffer *binder_alloc_new_buf_locked(struct binder_alloc *alloc,
 	if (end_page_addr > has_page_addr)
 		end_page_addr = has_page_addr;
 	ret = binder_update_page_range(alloc, 1,
-	    (void *)PAGE_ALIGN((uintptr_t)buffer->data), end_page_addr, NULL);
+	    (void *)PAGE_ALIGN((uintptr_t)buffer->data), end_page_addr);
 	if (ret)
 		return ERR_PTR(ret);
 
@@ -483,7 +483,7 @@ struct binder_buffer *binder_alloc_new_buf_locked(struct binder_alloc *alloc,
 err_alloc_buf_struct_failed:
 	binder_update_page_range(alloc, 0,
 				 (void *)PAGE_ALIGN((uintptr_t)buffer->data),
-				 end_page_addr, NULL);
+				 end_page_addr);
 	return ERR_PTR(-ENOMEM);
 }
 
@@ -567,8 +567,7 @@ static void binder_delete_free_buffer(struct binder_alloc *alloc,
 				   alloc->pid, buffer->data,
 				   prev->data, next->data);
 		binder_update_page_range(alloc, 0, buffer_start_page(buffer),
-					 buffer_start_page(buffer) + PAGE_SIZE,
-					 NULL);
+					 buffer_start_page(buffer) + PAGE_SIZE);
 	}
 	list_del(&buffer->entry);
 	kfree(buffer);
@@ -605,8 +604,7 @@ static void binder_free_buf_locked(struct binder_alloc *alloc,
 
 	binder_update_page_range(alloc, 0,
 		(void *)PAGE_ALIGN((uintptr_t)buffer->data),
-		(void *)(((uintptr_t)buffer->data + buffer_size) & PAGE_MASK),
-		NULL);
+		(void *)(((uintptr_t)buffer->data + buffer_size) & PAGE_MASK));
 
 	rb_erase(&buffer->rb_node, &alloc->allocated_buffers);
 	buffer->free = 1;
-- 
2.11.0 (Apple Git-81)

[PATCH 2/2] android: binder: Don't get mm from task

[Sherry Yang]

Use binder_alloc struct's mm_struct rather than getting
a reference to the mm struct through get_task_mm to
avoid a potential deadlock between lru lock, task lock and
dentry lock, since a thread can be holding the task lock
and the dentry lock while trying to acquire the lru lock.

Acked-by: Arve Hjønnevåg <arve@android.com>
Signed-off-by: Sherry Yang <sherryy@android.com>
---
 drivers/android/binder_alloc.c | 22 +++++++++-------------
 drivers/android/binder_alloc.h |  1 -
 2 files changed, 9 insertions(+), 14 deletions(-)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index b87ecf77f9d1..e283670695db 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -215,17 +215,12 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
 		}
 	}
 
-	if (need_mm)
-		mm = get_task_mm(alloc->tsk);
+	if (need_mm && mmget_not_zero(alloc->vma_vm_mm))
+		mm = alloc->vma_vm_mm;
 
 	if (mm) {
 		down_write(&mm->mmap_sem);
 		vma = alloc->vma;
-		if (vma && mm != alloc->vma_vm_mm) {
-			pr_err("%d: vma mm and task mm mismatch\n",
-				alloc->pid);
-			vma = NULL;
-		}
 	}
 
 	if (!vma && need_mm) {
@@ -718,6 +713,7 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
 	barrier();
 	alloc->vma = vma;
 	alloc->vma_vm_mm = vma->vm_mm;
+	mmgrab(alloc->vma_vm_mm);
 
 	return 0;
 
@@ -793,6 +789,8 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc)
 		vfree(alloc->buffer);
 	}
 	mutex_unlock(&alloc->mutex);
+	if (alloc->vma_vm_mm)
+		mmdrop(alloc->vma_vm_mm);
 
 	binder_alloc_debug(BINDER_DEBUG_OPEN_CLOSE,
 		     "%s: %d buffers %d, pages %d\n",
@@ -887,7 +885,6 @@ int binder_alloc_get_allocated_count(struct binder_alloc *alloc)
 void binder_alloc_vma_close(struct binder_alloc *alloc)
 {
 	WRITE_ONCE(alloc->vma, NULL);
-	WRITE_ONCE(alloc->vma_vm_mm, NULL);
 }
 
 /**
@@ -924,9 +921,9 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
 	page_addr = (uintptr_t)alloc->buffer + index * PAGE_SIZE;
 	vma = alloc->vma;
 	if (vma) {
-		mm = get_task_mm(alloc->tsk);
-		if (!mm)
-			goto err_get_task_mm_failed;
+		if (!mmget_not_zero(alloc->vma_vm_mm))
+			goto err_mmget;
+		mm = alloc->vma_vm_mm;
 		if (!down_write_trylock(&mm->mmap_sem))
 			goto err_down_write_mmap_sem_failed;
 	}
@@ -961,7 +958,7 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
 
 err_down_write_mmap_sem_failed:
 	mmput_async(mm);
-err_get_task_mm_failed:
+err_mmget:
 err_page_already_freed:
 	mutex_unlock(&alloc->mutex);
 err_get_alloc_mutex_failed:
@@ -1000,7 +997,6 @@ struct shrinker binder_shrinker = {
  */
 void binder_alloc_init(struct binder_alloc *alloc)
 {
-	alloc->tsk = current->group_leader;
 	alloc->pid = current->group_leader->pid;
 	mutex_init(&alloc->mutex);
 	INIT_LIST_HEAD(&alloc->buffers);
diff --git a/drivers/android/binder_alloc.h b/drivers/android/binder_alloc.h
index a3a3602c689c..2dd33b6df104 100644
--- a/drivers/android/binder_alloc.h
+++ b/drivers/android/binder_alloc.h
@@ -100,7 +100,6 @@ struct binder_lru_page {
  */
 struct binder_alloc {
 	struct mutex mutex;
-	struct task_struct *tsk;
 	struct vm_area_struct *vma;
 	struct mm_struct *vma_vm_mm;
 	void *buffer;
-- 
2.11.0 (Apple Git-81)

Make binder shrinker static and fix null dereference

[Sherry Yang]

This patch set makes binder shrinker static and fixes the null
pointer dereference in kernel debug message in binder_alloc.c.
The earlier patches from this email thread ("android: binder:
Remove unused vma argument" and "android: binder: Remove unused
vma argument") need to be applied before these two patches can
be applied cleanly.

    android: binder: Fix null ptr dereference in debug msg
    android: binder: Change binder_shrinker to static

drivers/android/binder_alloc.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

[PATCH 1/2] android: binder: Change binder_shrinker to static

[Sherry Yang]

binder_shrinker struct is not used anywhere outside of
binder_alloc.c and should be static.

Acked-by: Arve Hjønnevåg <arve@android.com>
Signed-off-by: Sherry Yang <sherryy@android.com>
---
 drivers/android/binder_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index e283670695db..47e2c032ad3d 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -982,7 +982,7 @@ binder_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
 	return ret;
 }
 
-struct shrinker binder_shrinker = {
+static struct shrinker binder_shrinker = {
 	.count_objects = binder_shrink_count,
 	.scan_objects = binder_shrink_scan,
 	.seeks = DEFAULT_SEEKS,
-- 
2.11.0 (Apple Git-81)

[PATCH 2/2] android: binder: Fix null ptr dereference in debug msg

[Sherry Yang]

Don't access next->data in kernel debug message when the
next buffer is null.

Acked-by: Arve Hjønnevåg <arve@android.com>
Signed-off-by: Sherry Yang <sherryy@android.com>
---
 drivers/android/binder_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 47e2c032ad3d..6f6f745605af 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -560,7 +560,7 @@ static void binder_delete_free_buffer(struct binder_alloc *alloc,
 		binder_alloc_debug(BINDER_DEBUG_BUFFER_ALLOC,
 				   "%d: merge free, buffer %pK do not share page with %pK or %pK\n",
 				   alloc->pid, buffer->data,
-				   prev->data, next->data);
+				   prev->data, next ? next->data : NULL);
 		binder_update_page_range(alloc, 0, buffer_start_page(buffer),
 					 buffer_start_page(buffer) + PAGE_SIZE);
 	}
-- 
2.11.0 (Apple Git-81)

Re: [PATCH 2/2] android: binder: Don't get mm from task

[Greg Kroah-Hartman]

On Sat, Sep 16, 2017 at 01:11:57AM -0400, Sherry Yang wrote:
> Use binder_alloc struct's mm_struct rather than getting
> a reference to the mm struct through get_task_mm to
> avoid a potential deadlock between lru lock, task lock and
> dentry lock, since a thread can be holding the task lock
> and the dentry lock while trying to acquire the lru lock.
> 
> Acked-by: Arve Hjønnevåg <arve@android.com>
> Signed-off-by: Sherry Yang <sherryy@android.com>
> ---
>  drivers/android/binder_alloc.c | 22 +++++++++-------------
>  drivers/android/binder_alloc.h |  1 -
>  2 files changed, 9 insertions(+), 14 deletions(-)

This seems to be needed for 4.14-final, so can you refresh it against my
char-misc-linus branch and resend it?

thanks,

greg k-h

Re: [PATCH 2/2] android: binder: Fix null ptr dereference in debug msg

[Greg Kroah-Hartman]

On Fri, Oct 06, 2017 at 04:12:06PM -0400, Sherry Yang wrote:
> Don't access next->data in kernel debug message when the
> next buffer is null.
> 
> Acked-by: Arve Hjønnevåg <arve@android.com>
> Signed-off-by: Sherry Yang <sherryy@android.com>
> ---
>  drivers/android/binder_alloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Same here, can you rebase and resend this one against char-misc-linus
and resend?

thanks,

greg k-h