* [PATCH 1/2] xenbus: req->body should be updated before req->state
@ 2020-03-03 1:58 Dongli Zhang
2020-03-03 1:58 ` [PATCH 2/2] xenbus: req->err " Dongli Zhang
2020-03-03 9:40 ` [Xen-devel] [PATCH 1/2] xenbus: req->body " Julien Grall
0 siblings, 2 replies; 6+ messages in thread
From: Dongli Zhang @ 2020-03-03 1:58 UTC (permalink / raw)
To: xen-devel, linux-kernel; +Cc: boris.ostrovsky, jgross, sstabellini, joe.jin
The req->body should be updated before req->state is updated and the
order should be guaranteed by a barrier.
Otherwise, read_reply() might return req->body = NULL.
Below is sample callstack when the issue is reproduced on purpose by
reordering the updates of req->body and req->state and adding delay in
code between updates of req->state and req->body.
[ 22.356105] general protection fault: 0000 [#1] SMP PTI
[ 22.361185] CPU: 2 PID: 52 Comm: xenwatch Not tainted 5.5.0xen+ #6
[ 22.366727] Hardware name: Xen HVM domU, BIOS ...
[ 22.372245] RIP: 0010:_parse_integer_fixup_radix+0x6/0x60
... ...
[ 22.392163] RSP: 0018:ffffb2d64023fdf0 EFLAGS: 00010246
[ 22.395933] RAX: 0000000000000000 RBX: 75746e7562755f6d RCX: 0000000000000000
[ 22.400871] RDX: 0000000000000000 RSI: ffffb2d64023fdfc RDI: 75746e7562755f6d
[ 22.405874] RBP: 0000000000000000 R08: 00000000000001e8 R09: 0000000000cdcdcd
[ 22.410945] R10: ffffb2d6402ffe00 R11: ffff9d95395eaeb0 R12: ffff9d9535935000
[ 22.417613] R13: ffff9d9526d4a000 R14: ffff9d9526f4f340 R15: ffff9d9537654000
[ 22.423726] FS: 0000000000000000(0000) GS:ffff9d953bc80000(0000) knlGS:0000000000000000
[ 22.429898] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 22.434342] CR2: 000000c4206a9000 CR3: 00000001ea3fc002 CR4: 00000000001606e0
[ 22.439645] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 22.444941] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 22.450342] Call Trace:
[ 22.452509] simple_strtoull+0x27/0x70
[ 22.455572] xenbus_transaction_start+0x31/0x50
[ 22.459104] netback_changed+0x76c/0xcc1 [xen_netfront]
[ 22.463279] ? find_watch+0x40/0x40
[ 22.466156] xenwatch_thread+0xb4/0x150
[ 22.469309] ? wait_woken+0x80/0x80
[ 22.472198] kthread+0x10e/0x130
[ 22.474925] ? kthread_park+0x80/0x80
[ 22.477946] ret_from_fork+0x35/0x40
[ 22.480968] Modules linked in: xen_kbdfront xen_fbfront(+) xen_netfront xen_blkfront
[ 22.486783] ---[ end trace a9222030a747c3f7 ]---
[ 22.490424] RIP: 0010:_parse_integer_fixup_radix+0x6/0x60
The "while" is changed to "do while" so that wait_event() is used as a
barrier.
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
---
drivers/xen/xenbus/xenbus_comms.c | 2 ++
drivers/xen/xenbus/xenbus_xs.c | 4 ++--
2 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c
index d239fc3c5e3d..852ed161fc2a 100644
--- a/drivers/xen/xenbus/xenbus_comms.c
+++ b/drivers/xen/xenbus/xenbus_comms.c
@@ -313,6 +313,8 @@ static int process_msg(void)
req->msg.type = state.msg.type;
req->msg.len = state.msg.len;
req->body = state.body;
+ /* write body, then update state */
+ virt_wmb();
req->state = xb_req_state_got_reply;
req->cb(req);
} else
diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c
index ddc18da61834..f5b0a6a72ad3 100644
--- a/drivers/xen/xenbus/xenbus_xs.c
+++ b/drivers/xen/xenbus/xenbus_xs.c
@@ -202,7 +202,7 @@ static bool test_reply(struct xb_req_data *req)
static void *read_reply(struct xb_req_data *req)
{
- while (req->state != xb_req_state_got_reply) {
+ do {
wait_event(req->wq, test_reply(req));
if (!xenbus_ok())
@@ -216,7 +216,7 @@ static void *read_reply(struct xb_req_data *req)
if (req->err)
return ERR_PTR(req->err);
- }
+ } while (req->state != xb_req_state_got_reply);
return req->body;
}
--
2.17.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH 2/2] xenbus: req->err should be updated before req->state
2020-03-03 1:58 [PATCH 1/2] xenbus: req->body should be updated before req->state Dongli Zhang
@ 2020-03-03 1:58 ` Dongli Zhang
2020-03-03 10:11 ` [Xen-devel] " Julien Grall
2020-03-03 9:40 ` [Xen-devel] [PATCH 1/2] xenbus: req->body " Julien Grall
1 sibling, 1 reply; 6+ messages in thread
From: Dongli Zhang @ 2020-03-03 1:58 UTC (permalink / raw)
To: xen-devel, linux-kernel; +Cc: boris.ostrovsky, jgross, sstabellini, joe.jin
This patch adds the barrier to guarantee that req->err is always updated
before req->state.
Otherwise, read_reply() would not return ERR_PTR(req->err) but
req->body, when process_writes()->xb_write() is failed.
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
---
drivers/xen/xenbus/xenbus_comms.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c
index 852ed161fc2a..eb5151fc8efa 100644
--- a/drivers/xen/xenbus/xenbus_comms.c
+++ b/drivers/xen/xenbus/xenbus_comms.c
@@ -397,6 +397,8 @@ static int process_writes(void)
if (state.req->state == xb_req_state_aborted)
kfree(state.req);
else {
+ /* write err, then update state */
+ virt_wmb();
state.req->state = xb_req_state_got_reply;
wake_up(&state.req->wq);
}
--
2.17.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [Xen-devel] [PATCH 1/2] xenbus: req->body should be updated before req->state
2020-03-03 1:58 [PATCH 1/2] xenbus: req->body should be updated before req->state Dongli Zhang
2020-03-03 1:58 ` [PATCH 2/2] xenbus: req->err " Dongli Zhang
@ 2020-03-03 9:40 ` Julien Grall
2020-03-03 17:36 ` dongli.zhang
1 sibling, 1 reply; 6+ messages in thread
From: Julien Grall @ 2020-03-03 9:40 UTC (permalink / raw)
To: Dongli Zhang, xen-devel, linux-kernel
Cc: jgross, boris.ostrovsky, sstabellini, joe.jin
Hi,
On 03/03/2020 01:58, Dongli Zhang wrote:
> The req->body should be updated before req->state is updated and the
> order should be guaranteed by a barrier.
>
> Otherwise, read_reply() might return req->body = NULL.
>
> Below is sample callstack when the issue is reproduced on purpose by
> reordering the updates of req->body and req->state and adding delay in
> code between updates of req->state and req->body.
>
> [ 22.356105] general protection fault: 0000 [#1] SMP PTI
> [ 22.361185] CPU: 2 PID: 52 Comm: xenwatch Not tainted 5.5.0xen+ #6
> [ 22.366727] Hardware name: Xen HVM domU, BIOS ...
> [ 22.372245] RIP: 0010:_parse_integer_fixup_radix+0x6/0x60
> ... ...
> [ 22.392163] RSP: 0018:ffffb2d64023fdf0 EFLAGS: 00010246
> [ 22.395933] RAX: 0000000000000000 RBX: 75746e7562755f6d RCX: 0000000000000000
> [ 22.400871] RDX: 0000000000000000 RSI: ffffb2d64023fdfc RDI: 75746e7562755f6d
> [ 22.405874] RBP: 0000000000000000 R08: 00000000000001e8 R09: 0000000000cdcdcd
> [ 22.410945] R10: ffffb2d6402ffe00 R11: ffff9d95395eaeb0 R12: ffff9d9535935000
> [ 22.417613] R13: ffff9d9526d4a000 R14: ffff9d9526f4f340 R15: ffff9d9537654000
> [ 22.423726] FS: 0000000000000000(0000) GS:ffff9d953bc80000(0000) knlGS:0000000000000000
> [ 22.429898] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 22.434342] CR2: 000000c4206a9000 CR3: 00000001ea3fc002 CR4: 00000000001606e0
> [ 22.439645] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 22.444941] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [ 22.450342] Call Trace:
> [ 22.452509] simple_strtoull+0x27/0x70
> [ 22.455572] xenbus_transaction_start+0x31/0x50
> [ 22.459104] netback_changed+0x76c/0xcc1 [xen_netfront]
> [ 22.463279] ? find_watch+0x40/0x40
> [ 22.466156] xenwatch_thread+0xb4/0x150
> [ 22.469309] ? wait_woken+0x80/0x80
> [ 22.472198] kthread+0x10e/0x130
> [ 22.474925] ? kthread_park+0x80/0x80
> [ 22.477946] ret_from_fork+0x35/0x40
> [ 22.480968] Modules linked in: xen_kbdfront xen_fbfront(+) xen_netfront xen_blkfront
> [ 22.486783] ---[ end trace a9222030a747c3f7 ]---
> [ 22.490424] RIP: 0010:_parse_integer_fixup_radix+0x6/0x60
>
> The "while" is changed to "do while" so that wait_event() is used as a
> barrier.
The correct barrier for read_reply() should be virt_rmb(). While on x86,
this is equivalent to barrier(), on Arm this will be a dmb(ish) to
prevent the processor re-ordering memory access.
Therefore the barrier in test_reply() (called by wait_event()) is not
going to be sufficient for Arm.
>
> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
> ---
> drivers/xen/xenbus/xenbus_comms.c | 2 ++
> drivers/xen/xenbus/xenbus_xs.c | 4 ++--
> 2 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c
> index d239fc3c5e3d..852ed161fc2a 100644
> --- a/drivers/xen/xenbus/xenbus_comms.c
> +++ b/drivers/xen/xenbus/xenbus_comms.c
> @@ -313,6 +313,8 @@ static int process_msg(void)
> req->msg.type = state.msg.type;
> req->msg.len = state.msg.len;
> req->body = state.body;
> + /* write body, then update state */
> + virt_wmb();
> req->state = xb_req_state_got_reply;
> req->cb(req);
> } else
> diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c
> index ddc18da61834..f5b0a6a72ad3 100644
> --- a/drivers/xen/xenbus/xenbus_xs.c
> +++ b/drivers/xen/xenbus/xenbus_xs.c
> @@ -202,7 +202,7 @@ static bool test_reply(struct xb_req_data *req)
>
> static void *read_reply(struct xb_req_data *req)
> {
> - while (req->state != xb_req_state_got_reply) {
> + do {
> wait_event(req->wq, test_reply(req));
>
> if (!xenbus_ok())
> @@ -216,7 +216,7 @@ static void *read_reply(struct xb_req_data *req)
> if (req->err)
> return ERR_PTR(req->err);
>
> - }
> + } while (req->state != xb_req_state_got_reply);
>
> return req->body;
> }
>
Cheers,
--
Julien Grall
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Xen-devel] [PATCH 2/2] xenbus: req->err should be updated before req->state
2020-03-03 1:58 ` [PATCH 2/2] xenbus: req->err " Dongli Zhang
@ 2020-03-03 10:11 ` Julien Grall
0 siblings, 0 replies; 6+ messages in thread
From: Julien Grall @ 2020-03-03 10:11 UTC (permalink / raw)
To: Dongli Zhang, xen-devel, linux-kernel
Cc: jgross, boris.ostrovsky, sstabellini, joe.jin
Hi,
On 03/03/2020 01:58, Dongli Zhang wrote:
> This patch adds the barrier to guarantee that req->err is always updated
> before req->state.
>
> Otherwise, read_reply() would not return ERR_PTR(req->err) but
> req->body, when process_writes()->xb_write() is failed.
The memory barrier below looks good. However, as mentionned in patch #1,
barrier() is not the correct barrier to pair with virt_wmb().
>
> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
> ---
> drivers/xen/xenbus/xenbus_comms.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c
> index 852ed161fc2a..eb5151fc8efa 100644
> --- a/drivers/xen/xenbus/xenbus_comms.c
> +++ b/drivers/xen/xenbus/xenbus_comms.c
> @@ -397,6 +397,8 @@ static int process_writes(void)
> if (state.req->state == xb_req_state_aborted)
> kfree(state.req);
> else {
> + /* write err, then update state */
> + virt_wmb();
> state.req->state = xb_req_state_got_reply;
> wake_up(&state.req->wq);
> }
>
Cheers,
--
Julien Grall
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Xen-devel] [PATCH 1/2] xenbus: req->body should be updated before req->state
2020-03-03 9:40 ` [Xen-devel] [PATCH 1/2] xenbus: req->body " Julien Grall
@ 2020-03-03 17:36 ` dongli.zhang
2020-03-03 18:32 ` Julien Grall
0 siblings, 1 reply; 6+ messages in thread
From: dongli.zhang @ 2020-03-03 17:36 UTC (permalink / raw)
To: Julien Grall, xen-devel, linux-kernel
Cc: jgross, boris.ostrovsky, sstabellini, joe.jin
On 3/3/20 1:40 AM, Julien Grall wrote:
> Hi,
>
> On 03/03/2020 01:58, Dongli Zhang wrote:
>> The req->body should be updated before req->state is updated and the
>> order should be guaranteed by a barrier.
>>
>> Otherwise, read_reply() might return req->body = NULL.
>>
>> Below is sample callstack when the issue is reproduced on purpose by
>> reordering the updates of req->body and req->state and adding delay in
>> code between updates of req->state and req->body.
>>
>> [ 22.356105] general protection fault: 0000 [#1] SMP PTI
>> [ 22.361185] CPU: 2 PID: 52 Comm: xenwatch Not tainted 5.5.0xen+ #6
>> [ 22.366727] Hardware name: Xen HVM domU, BIOS ...
>> [ 22.372245] RIP: 0010:_parse_integer_fixup_radix+0x6/0x60
>> ... ...
>> [ 22.392163] RSP: 0018:ffffb2d64023fdf0 EFLAGS: 00010246
>> [ 22.395933] RAX: 0000000000000000 RBX: 75746e7562755f6d RCX: 0000000000000000
>> [ 22.400871] RDX: 0000000000000000 RSI: ffffb2d64023fdfc RDI: 75746e7562755f6d
>> [ 22.405874] RBP: 0000000000000000 R08: 00000000000001e8 R09: 0000000000cdcdcd
>> [ 22.410945] R10: ffffb2d6402ffe00 R11: ffff9d95395eaeb0 R12: ffff9d9535935000
>> [ 22.417613] R13: ffff9d9526d4a000 R14: ffff9d9526f4f340 R15: ffff9d9537654000
>> [ 22.423726] FS: 0000000000000000(0000) GS:ffff9d953bc80000(0000)
>> knlGS:0000000000000000
>> [ 22.429898] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [ 22.434342] CR2: 000000c4206a9000 CR3: 00000001ea3fc002 CR4: 00000000001606e0
>> [ 22.439645] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> [ 22.444941] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> [ 22.450342] Call Trace:
>> [ 22.452509] simple_strtoull+0x27/0x70
>> [ 22.455572] xenbus_transaction_start+0x31/0x50
>> [ 22.459104] netback_changed+0x76c/0xcc1 [xen_netfront]
>> [ 22.463279] ? find_watch+0x40/0x40
>> [ 22.466156] xenwatch_thread+0xb4/0x150
>> [ 22.469309] ? wait_woken+0x80/0x80
>> [ 22.472198] kthread+0x10e/0x130
>> [ 22.474925] ? kthread_park+0x80/0x80
>> [ 22.477946] ret_from_fork+0x35/0x40
>> [ 22.480968] Modules linked in: xen_kbdfront xen_fbfront(+) xen_netfront
>> xen_blkfront
>> [ 22.486783] ---[ end trace a9222030a747c3f7 ]---
>> [ 22.490424] RIP: 0010:_parse_integer_fixup_radix+0x6/0x60
>>
>> The "while" is changed to "do while" so that wait_event() is used as a
>> barrier.
>
> The correct barrier for read_reply() should be virt_rmb(). While on x86, this is
> equivalent to barrier(), on Arm this will be a dmb(ish) to prevent the processor
> re-ordering memory access.
>
> Therefore the barrier in test_reply() (called by wait_event()) is not going to
> be sufficient for Arm.
Sorry that I just erroneously thought wait_event() would be used as read barrier.
I would change barrier() to virt_rmb() for read_reply() in v2.
Thank you very much!
Dongli Zhang
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Xen-devel] [PATCH 1/2] xenbus: req->body should be updated before req->state
2020-03-03 17:36 ` dongli.zhang
@ 2020-03-03 18:32 ` Julien Grall
0 siblings, 0 replies; 6+ messages in thread
From: Julien Grall @ 2020-03-03 18:32 UTC (permalink / raw)
To: dongli.zhang, xen-devel, linux-kernel
Cc: jgross, boris.ostrovsky, sstabellini, joe.jin
Hi,
On 03/03/2020 17:36, dongli.zhang@oracle.com wrote:
>
>
> On 3/3/20 1:40 AM, Julien Grall wrote:
>> Hi,
>>
>> On 03/03/2020 01:58, Dongli Zhang wrote:
>>> The req->body should be updated before req->state is updated and the
>>> order should be guaranteed by a barrier.
>>>
>>> Otherwise, read_reply() might return req->body = NULL.
>>>
>>> Below is sample callstack when the issue is reproduced on purpose by
>>> reordering the updates of req->body and req->state and adding delay in
>>> code between updates of req->state and req->body.
>>>
>>> [ 22.356105] general protection fault: 0000 [#1] SMP PTI
>>> [ 22.361185] CPU: 2 PID: 52 Comm: xenwatch Not tainted 5.5.0xen+ #6
>>> [ 22.366727] Hardware name: Xen HVM domU, BIOS ...
>>> [ 22.372245] RIP: 0010:_parse_integer_fixup_radix+0x6/0x60
>>> ... ...
>>> [ 22.392163] RSP: 0018:ffffb2d64023fdf0 EFLAGS: 00010246
>>> [ 22.395933] RAX: 0000000000000000 RBX: 75746e7562755f6d RCX: 0000000000000000
>>> [ 22.400871] RDX: 0000000000000000 RSI: ffffb2d64023fdfc RDI: 75746e7562755f6d
>>> [ 22.405874] RBP: 0000000000000000 R08: 00000000000001e8 R09: 0000000000cdcdcd
>>> [ 22.410945] R10: ffffb2d6402ffe00 R11: ffff9d95395eaeb0 R12: ffff9d9535935000
>>> [ 22.417613] R13: ffff9d9526d4a000 R14: ffff9d9526f4f340 R15: ffff9d9537654000
>>> [ 22.423726] FS: 0000000000000000(0000) GS:ffff9d953bc80000(0000)
>>> knlGS:0000000000000000
>>> [ 22.429898] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> [ 22.434342] CR2: 000000c4206a9000 CR3: 00000001ea3fc002 CR4: 00000000001606e0
>>> [ 22.439645] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>> [ 22.444941] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>> [ 22.450342] Call Trace:
>>> [ 22.452509] simple_strtoull+0x27/0x70
>>> [ 22.455572] xenbus_transaction_start+0x31/0x50
>>> [ 22.459104] netback_changed+0x76c/0xcc1 [xen_netfront]
>>> [ 22.463279] ? find_watch+0x40/0x40
>>> [ 22.466156] xenwatch_thread+0xb4/0x150
>>> [ 22.469309] ? wait_woken+0x80/0x80
>>> [ 22.472198] kthread+0x10e/0x130
>>> [ 22.474925] ? kthread_park+0x80/0x80
>>> [ 22.477946] ret_from_fork+0x35/0x40
>>> [ 22.480968] Modules linked in: xen_kbdfront xen_fbfront(+) xen_netfront
>>> xen_blkfront
>>> [ 22.486783] ---[ end trace a9222030a747c3f7 ]---
>>> [ 22.490424] RIP: 0010:_parse_integer_fixup_radix+0x6/0x60
>>>
>>> The "while" is changed to "do while" so that wait_event() is used as a
>>> barrier.
>>
>> The correct barrier for read_reply() should be virt_rmb(). While on x86, this is
>> equivalent to barrier(), on Arm this will be a dmb(ish) to prevent the processor
>> re-ordering memory access.
>>
>> Therefore the barrier in test_reply() (called by wait_event()) is not going to
>> be sufficient for Arm.
>
> Sorry that I just erroneously thought wait_event() would be used as read barrier.
I was also kind of expecting wait_event() to contain a memory barrier.
But it does not at least if condition is valid before waiting.
Cheers,
--
Julien Grall
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2020-03-03 18:32 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-03-03 1:58 [PATCH 1/2] xenbus: req->body should be updated before req->state Dongli Zhang
2020-03-03 1:58 ` [PATCH 2/2] xenbus: req->err " Dongli Zhang
2020-03-03 10:11 ` [Xen-devel] " Julien Grall
2020-03-03 9:40 ` [Xen-devel] [PATCH 1/2] xenbus: req->body " Julien Grall
2020-03-03 17:36 ` dongli.zhang
2020-03-03 18:32 ` Julien Grall
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