* Re: [PATCH 1/1] xen-blkback: do not wake up shutdown_wq after xen_blkif_schedule() is stopped
@ 2019-01-17 2:10 ` Dongli Zhang
0 siblings, 0 replies; 11+ messages in thread
From: Dongli Zhang @ 2019-01-17 2:10 UTC (permalink / raw)
To: Roger Pau Monné
Cc: linux-block, xen-devel, konrad.wilk, axboe, linux-kernel
Hi Roger,
On 2019/1/16 下午10:52, Roger Pau Monné wrote:
> On Wed, Jan 16, 2019 at 09:47:41PM +0800, Dongli Zhang wrote:
>> There is no need to wake up xen_blkif_schedule() as kthread_stop() is able
>> to already wake up the kernel thread.
>>
>> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
>> ---
>> drivers/block/xen-blkback/xenbus.c | 4 +---
>> 1 file changed, 1 insertion(+), 3 deletions(-)
>>
>> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
>> index a4bc74e..37ac59e 100644
>> --- a/drivers/block/xen-blkback/xenbus.c
>> +++ b/drivers/block/xen-blkback/xenbus.c
>> @@ -254,10 +254,8 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif)
>> if (!ring->active)
>> continue;
>>
>> - if (ring->xenblkd) {
>> + if (ring->xenblkd)
>> kthread_stop(ring->xenblkd);
>> - wake_up(&ring->shutdown_wq);
>
> I've now realized that shutdown_wq is basically useless, and should be
> removed, could you please do it in this patch?
I do not think shutdown_wq is useless.
It is used to halt the xen_blkif_schedule() kthread when
RING_REQUEST_PROD_OVERFLOW() returns true in __do_block_io_op():
1121 static int
1122 __do_block_io_op(struct xen_blkif_ring *ring)
... ...
1134 if (RING_REQUEST_PROD_OVERFLOW(&blk_rings->common, rp)) {
1135 rc = blk_rings->common.rsp_prod_pvt;
1136 pr_warn("Frontend provided bogus ring requests (%d - %d =
%d). Halting ring processing on dev=%04x\n",
1137 rp, rc, rp - rc, ring->blkif->vbd.pdevice);
1138 return -EACCES;
1139 }
If there is bogus/invalid ring requests, __do_block_io_op() would return -EACCES
without modifying prod/cons index.
Without shutdown_wq (just simply assuming we remove the below code without
handling -EACCES in xen_blkif_schedule()), the kernel thread would continue the
while loop.
648 if (ret == -EACCES)
649 wait_event_interruptible(ring->shutdown_wq,
650 kthread_should_stop());
If xen_blkif_be_int() is triggered again (let's assume there is no optimization
on guest part and guest would send event for every request it puts on ring
buffer), we may come to do_block_io_op() again.
As the prod/cons index are not modified last time the code runs into
do_block_io_op() to process bogus request, we would hit the bogus request issue
again.
With shutdown_wq, the kernel kthread is blocked forever until such queue/ring is
destroyed. If we remove shutdown_wq, we are changing the policy to handle bogus
requests on ring buffer?
Please correct me if my understanding is wrong.
Thank you very much!
Dongli Zhang
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel
^ permalink raw reply [flat|nested] 11+ messages in thread* Re: [PATCH 1/1] xen-blkback: do not wake up shutdown_wq after xen_blkif_schedule() is stopped
2019-01-17 2:10 ` Dongli Zhang
(?)
@ 2019-01-17 8:20 ` Roger Pau Monné
-1 siblings, 0 replies; 11+ messages in thread
From: Roger Pau Monné @ 2019-01-17 8:20 UTC (permalink / raw)
To: Dongli Zhang; +Cc: linux-block, xen-devel, konrad.wilk, axboe, linux-kernel
On Thu, Jan 17, 2019 at 10:10:00AM +0800, Dongli Zhang wrote:
> Hi Roger,
>
> On 2019/1/16 下午10:52, Roger Pau Monné wrote:
> > On Wed, Jan 16, 2019 at 09:47:41PM +0800, Dongli Zhang wrote:
> >> There is no need to wake up xen_blkif_schedule() as kthread_stop() is able
> >> to already wake up the kernel thread.
> >>
> >> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
> >> ---
> >> drivers/block/xen-blkback/xenbus.c | 4 +---
> >> 1 file changed, 1 insertion(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
> >> index a4bc74e..37ac59e 100644
> >> --- a/drivers/block/xen-blkback/xenbus.c
> >> +++ b/drivers/block/xen-blkback/xenbus.c
> >> @@ -254,10 +254,8 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif)
> >> if (!ring->active)
> >> continue;
> >>
> >> - if (ring->xenblkd) {
> >> + if (ring->xenblkd)
> >> kthread_stop(ring->xenblkd);
> >> - wake_up(&ring->shutdown_wq);
> >
> > I've now realized that shutdown_wq is basically useless, and should be
> > removed, could you please do it in this patch?
>
> I do not think shutdown_wq is useless.
>
> It is used to halt the xen_blkif_schedule() kthread when
> RING_REQUEST_PROD_OVERFLOW() returns true in __do_block_io_op():
>
> 1121 static int
> 1122 __do_block_io_op(struct xen_blkif_ring *ring)
> ... ...
> 1134 if (RING_REQUEST_PROD_OVERFLOW(&blk_rings->common, rp)) {
> 1135 rc = blk_rings->common.rsp_prod_pvt;
> 1136 pr_warn("Frontend provided bogus ring requests (%d - %d =
> %d). Halting ring processing on dev=%04x\n",
> 1137 rp, rc, rp - rc, ring->blkif->vbd.pdevice);
> 1138 return -EACCES;
> 1139 }
>
>
> If there is bogus/invalid ring requests, __do_block_io_op() would return -EACCES
> without modifying prod/cons index.
>
> Without shutdown_wq (just simply assuming we remove the below code without
> handling -EACCES in xen_blkif_schedule()), the kernel thread would continue the
> while loop.
>
> 648 if (ret == -EACCES)
> 649 wait_event_interruptible(ring->shutdown_wq,
> 650 kthread_should_stop());
>
>
> If xen_blkif_be_int() is triggered again (let's assume there is no optimization
> on guest part and guest would send event for every request it puts on ring
> buffer), we may come to do_block_io_op() again.
>
>
> As the prod/cons index are not modified last time the code runs into
> do_block_io_op() to process bogus request, we would hit the bogus request issue
> again.
>
>
> With shutdown_wq, the kernel kthread is blocked forever until such queue/ring is
> destroyed. If we remove shutdown_wq, we are changing the policy to handle bogus
> requests on ring buffer?
AFAICT the only wakeup call to shutdown_wq is removed in this patch,
hence waiting on it seems useless. I would replace the
wait_event_interruptible call in xen_blkif_schedule with a break, so
that the kthread ends as soon as a bogus request is found. I think
there's no point in waiting for xen_blkif_disconnect to stop the
kthread.
Thanks, Roger.
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel
^ permalink raw reply [flat|nested] 11+ messages in thread* Re: [Xen-devel] [PATCH 1/1] xen-blkback: do not wake up shutdown_wq after xen_blkif_schedule() is stopped
2019-01-17 2:10 ` Dongli Zhang
(?)
(?)
@ 2019-01-17 8:20 ` Roger Pau Monné
2019-01-17 10:23 ` Dongli Zhang
2019-01-17 10:23 ` Dongli Zhang
-1 siblings, 2 replies; 11+ messages in thread
From: Roger Pau Monné @ 2019-01-17 8:20 UTC (permalink / raw)
To: Dongli Zhang; +Cc: linux-block, xen-devel, axboe, linux-kernel, konrad.wilk
On Thu, Jan 17, 2019 at 10:10:00AM +0800, Dongli Zhang wrote:
> Hi Roger,
>
> On 2019/1/16 下午10:52, Roger Pau Monné wrote:
> > On Wed, Jan 16, 2019 at 09:47:41PM +0800, Dongli Zhang wrote:
> >> There is no need to wake up xen_blkif_schedule() as kthread_stop() is able
> >> to already wake up the kernel thread.
> >>
> >> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
> >> ---
> >> drivers/block/xen-blkback/xenbus.c | 4 +---
> >> 1 file changed, 1 insertion(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
> >> index a4bc74e..37ac59e 100644
> >> --- a/drivers/block/xen-blkback/xenbus.c
> >> +++ b/drivers/block/xen-blkback/xenbus.c
> >> @@ -254,10 +254,8 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif)
> >> if (!ring->active)
> >> continue;
> >>
> >> - if (ring->xenblkd) {
> >> + if (ring->xenblkd)
> >> kthread_stop(ring->xenblkd);
> >> - wake_up(&ring->shutdown_wq);
> >
> > I've now realized that shutdown_wq is basically useless, and should be
> > removed, could you please do it in this patch?
>
> I do not think shutdown_wq is useless.
>
> It is used to halt the xen_blkif_schedule() kthread when
> RING_REQUEST_PROD_OVERFLOW() returns true in __do_block_io_op():
>
> 1121 static int
> 1122 __do_block_io_op(struct xen_blkif_ring *ring)
> ... ...
> 1134 if (RING_REQUEST_PROD_OVERFLOW(&blk_rings->common, rp)) {
> 1135 rc = blk_rings->common.rsp_prod_pvt;
> 1136 pr_warn("Frontend provided bogus ring requests (%d - %d =
> %d). Halting ring processing on dev=%04x\n",
> 1137 rp, rc, rp - rc, ring->blkif->vbd.pdevice);
> 1138 return -EACCES;
> 1139 }
>
>
> If there is bogus/invalid ring requests, __do_block_io_op() would return -EACCES
> without modifying prod/cons index.
>
> Without shutdown_wq (just simply assuming we remove the below code without
> handling -EACCES in xen_blkif_schedule()), the kernel thread would continue the
> while loop.
>
> 648 if (ret == -EACCES)
> 649 wait_event_interruptible(ring->shutdown_wq,
> 650 kthread_should_stop());
>
>
> If xen_blkif_be_int() is triggered again (let's assume there is no optimization
> on guest part and guest would send event for every request it puts on ring
> buffer), we may come to do_block_io_op() again.
>
>
> As the prod/cons index are not modified last time the code runs into
> do_block_io_op() to process bogus request, we would hit the bogus request issue
> again.
>
>
> With shutdown_wq, the kernel kthread is blocked forever until such queue/ring is
> destroyed. If we remove shutdown_wq, we are changing the policy to handle bogus
> requests on ring buffer?
AFAICT the only wakeup call to shutdown_wq is removed in this patch,
hence waiting on it seems useless. I would replace the
wait_event_interruptible call in xen_blkif_schedule with a break, so
that the kthread ends as soon as a bogus request is found. I think
there's no point in waiting for xen_blkif_disconnect to stop the
kthread.
Thanks, Roger.
^ permalink raw reply [flat|nested] 11+ messages in thread* Re: [Xen-devel] [PATCH 1/1] xen-blkback: do not wake up shutdown_wq after xen_blkif_schedule() is stopped
2019-01-17 8:20 ` [Xen-devel] " Roger Pau Monné
@ 2019-01-17 10:23 ` Dongli Zhang
2019-01-17 10:23 ` Dongli Zhang
1 sibling, 0 replies; 11+ messages in thread
From: Dongli Zhang @ 2019-01-17 10:23 UTC (permalink / raw)
To: Roger Pau Monné
Cc: linux-block, xen-devel, axboe, linux-kernel, konrad.wilk
Hi Roger,
On 01/17/2019 04:20 PM, Roger Pau Monné wrote:
> On Thu, Jan 17, 2019 at 10:10:00AM +0800, Dongli Zhang wrote:
>> Hi Roger,
>>
>> On 2019/1/16 下午10:52, Roger Pau Monné wrote:
>>> On Wed, Jan 16, 2019 at 09:47:41PM +0800, Dongli Zhang wrote:
>>>> There is no need to wake up xen_blkif_schedule() as kthread_stop() is able
>>>> to already wake up the kernel thread.
>>>>
>>>> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
>>>> ---
>>>> drivers/block/xen-blkback/xenbus.c | 4 +---
>>>> 1 file changed, 1 insertion(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
>>>> index a4bc74e..37ac59e 100644
>>>> --- a/drivers/block/xen-blkback/xenbus.c
>>>> +++ b/drivers/block/xen-blkback/xenbus.c
>>>> @@ -254,10 +254,8 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif)
>>>> if (!ring->active)
>>>> continue;
>>>>
>>>> - if (ring->xenblkd) {
>>>> + if (ring->xenblkd)
>>>> kthread_stop(ring->xenblkd);
>>>> - wake_up(&ring->shutdown_wq);
>>>
>>> I've now realized that shutdown_wq is basically useless, and should be
>>> removed, could you please do it in this patch?
>>
>> I do not think shutdown_wq is useless.
>>
>> It is used to halt the xen_blkif_schedule() kthread when
>> RING_REQUEST_PROD_OVERFLOW() returns true in __do_block_io_op():
>>
>> 1121 static int
>> 1122 __do_block_io_op(struct xen_blkif_ring *ring)
>> ... ...
>> 1134 if (RING_REQUEST_PROD_OVERFLOW(&blk_rings->common, rp)) {
>> 1135 rc = blk_rings->common.rsp_prod_pvt;
>> 1136 pr_warn("Frontend provided bogus ring requests (%d - %d =
>> %d). Halting ring processing on dev=%04x\n",
>> 1137 rp, rc, rp - rc, ring->blkif->vbd.pdevice);
>> 1138 return -EACCES;
>> 1139 }
>>
>>
>> If there is bogus/invalid ring requests, __do_block_io_op() would return -EACCES
>> without modifying prod/cons index.
>>
>> Without shutdown_wq (just simply assuming we remove the below code without
>> handling -EACCES in xen_blkif_schedule()), the kernel thread would continue the
>> while loop.
>>
>> 648 if (ret == -EACCES)
>> 649 wait_event_interruptible(ring->shutdown_wq,
>> 650 kthread_should_stop());
>>
>>
>> If xen_blkif_be_int() is triggered again (let's assume there is no optimization
>> on guest part and guest would send event for every request it puts on ring
>> buffer), we may come to do_block_io_op() again.
>>
>>
>> As the prod/cons index are not modified last time the code runs into
>> do_block_io_op() to process bogus request, we would hit the bogus request issue
>> again.
>>
>>
>> With shutdown_wq, the kernel kthread is blocked forever until such queue/ring is
>> destroyed. If we remove shutdown_wq, we are changing the policy to handle bogus
>> requests on ring buffer?
>
> AFAICT the only wakeup call to shutdown_wq is removed in this patch,
> hence waiting on it seems useless. I would replace the
> wait_event_interruptible call in xen_blkif_schedule with a break, so
> that the kthread ends as soon as a bogus request is found. I think
> there's no point in waiting for xen_blkif_disconnect to stop the
> kthread.
>
> Thanks, Roger.
>
My fault. The shutdown_wq is useless. I think I was going to say
wait_event_interruptible() is useful as it is used to halt the kthread when
there is bogus request.
It is fine to replace wait_event_interruptible with a break to exit immediately
when there is bogus request.
Thank you very much!
Dongli Zhang
^ permalink raw reply [flat|nested] 11+ messages in thread* Re: [PATCH 1/1] xen-blkback: do not wake up shutdown_wq after xen_blkif_schedule() is stopped
2019-01-17 8:20 ` [Xen-devel] " Roger Pau Monné
2019-01-17 10:23 ` Dongli Zhang
@ 2019-01-17 10:23 ` Dongli Zhang
1 sibling, 0 replies; 11+ messages in thread
From: Dongli Zhang @ 2019-01-17 10:23 UTC (permalink / raw)
To: Roger Pau Monné
Cc: linux-block, xen-devel, konrad.wilk, axboe, linux-kernel
Hi Roger,
On 01/17/2019 04:20 PM, Roger Pau Monné wrote:
> On Thu, Jan 17, 2019 at 10:10:00AM +0800, Dongli Zhang wrote:
>> Hi Roger,
>>
>> On 2019/1/16 下午10:52, Roger Pau Monné wrote:
>>> On Wed, Jan 16, 2019 at 09:47:41PM +0800, Dongli Zhang wrote:
>>>> There is no need to wake up xen_blkif_schedule() as kthread_stop() is able
>>>> to already wake up the kernel thread.
>>>>
>>>> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
>>>> ---
>>>> drivers/block/xen-blkback/xenbus.c | 4 +---
>>>> 1 file changed, 1 insertion(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
>>>> index a4bc74e..37ac59e 100644
>>>> --- a/drivers/block/xen-blkback/xenbus.c
>>>> +++ b/drivers/block/xen-blkback/xenbus.c
>>>> @@ -254,10 +254,8 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif)
>>>> if (!ring->active)
>>>> continue;
>>>>
>>>> - if (ring->xenblkd) {
>>>> + if (ring->xenblkd)
>>>> kthread_stop(ring->xenblkd);
>>>> - wake_up(&ring->shutdown_wq);
>>>
>>> I've now realized that shutdown_wq is basically useless, and should be
>>> removed, could you please do it in this patch?
>>
>> I do not think shutdown_wq is useless.
>>
>> It is used to halt the xen_blkif_schedule() kthread when
>> RING_REQUEST_PROD_OVERFLOW() returns true in __do_block_io_op():
>>
>> 1121 static int
>> 1122 __do_block_io_op(struct xen_blkif_ring *ring)
>> ... ...
>> 1134 if (RING_REQUEST_PROD_OVERFLOW(&blk_rings->common, rp)) {
>> 1135 rc = blk_rings->common.rsp_prod_pvt;
>> 1136 pr_warn("Frontend provided bogus ring requests (%d - %d =
>> %d). Halting ring processing on dev=%04x\n",
>> 1137 rp, rc, rp - rc, ring->blkif->vbd.pdevice);
>> 1138 return -EACCES;
>> 1139 }
>>
>>
>> If there is bogus/invalid ring requests, __do_block_io_op() would return -EACCES
>> without modifying prod/cons index.
>>
>> Without shutdown_wq (just simply assuming we remove the below code without
>> handling -EACCES in xen_blkif_schedule()), the kernel thread would continue the
>> while loop.
>>
>> 648 if (ret == -EACCES)
>> 649 wait_event_interruptible(ring->shutdown_wq,
>> 650 kthread_should_stop());
>>
>>
>> If xen_blkif_be_int() is triggered again (let's assume there is no optimization
>> on guest part and guest would send event for every request it puts on ring
>> buffer), we may come to do_block_io_op() again.
>>
>>
>> As the prod/cons index are not modified last time the code runs into
>> do_block_io_op() to process bogus request, we would hit the bogus request issue
>> again.
>>
>>
>> With shutdown_wq, the kernel kthread is blocked forever until such queue/ring is
>> destroyed. If we remove shutdown_wq, we are changing the policy to handle bogus
>> requests on ring buffer?
>
> AFAICT the only wakeup call to shutdown_wq is removed in this patch,
> hence waiting on it seems useless. I would replace the
> wait_event_interruptible call in xen_blkif_schedule with a break, so
> that the kthread ends as soon as a bogus request is found. I think
> there's no point in waiting for xen_blkif_disconnect to stop the
> kthread.
>
> Thanks, Roger.
>
My fault. The shutdown_wq is useless. I think I was going to say
wait_event_interruptible() is useful as it is used to halt the kthread when
there is bogus request.
It is fine to replace wait_event_interruptible with a break to exit immediately
when there is bogus request.
Thank you very much!
Dongli Zhang
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel
^ permalink raw reply [flat|nested] 11+ messages in thread