* [Qemu-devel] [PATCH v2] block: make BDRV_POLL_WHILE() re-entrancy safe
@ 2018-03-07 12:46 Stefan Hajnoczi
2018-03-07 23:19 ` Eric Blake
2018-03-12 11:07 ` [Qemu-devel] [Qemu-block] " Stefan Hajnoczi
0 siblings, 2 replies; 3+ messages in thread
From: Stefan Hajnoczi @ 2018-03-07 12:46 UTC (permalink / raw)
To: qemu-devel
Cc: Max Reitz, Kevin Wolf, qemu-block, Paolo Bonzini,
Stefan Hajnoczi, Fam Zheng, fuweiwei (C)
Nested BDRV_POLL_WHILE() calls can occur. Currently
assert(!wait_->wakeup) fails in AIO_WAIT_WHILE() when this happens.
This patch converts the bool wait_->need_kick flag to an unsigned
wait_->num_waiters counter.
Nesting works correctly because outer AIO_WAIT_WHILE() callers evaluate
the condition again after the inner caller completes (invoking the inner
caller counts as aio_poll() progress).
Reported-by: "fuweiwei (C)" <fuweiwei2@huawei.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
v2:
* Rebase onto qemu.git/master now that AIO_WAIT_WHILE() has landed
[Kevin]
include/block/aio-wait.h | 61 ++++++++++++++++++++++++------------------------
util/aio-wait.c | 2 +-
2 files changed, 31 insertions(+), 32 deletions(-)
diff --git a/include/block/aio-wait.h b/include/block/aio-wait.h
index a48c744fa8..74cde07bef 100644
--- a/include/block/aio-wait.h
+++ b/include/block/aio-wait.h
@@ -50,8 +50,8 @@
* }
*/
typedef struct {
- /* Is the main loop waiting for a kick? Accessed with atomic ops. */
- bool need_kick;
+ /* Number of waiting AIO_WAIT_WHILE() callers. Accessed with atomic ops. */
+ unsigned num_waiters;
} AioWait;
/**
@@ -71,35 +71,34 @@ typedef struct {
* wait on conditions between two IOThreads since that could lead to deadlock,
* go via the main loop instead.
*/
-#define AIO_WAIT_WHILE(wait, ctx, cond) ({ \
- bool waited_ = false; \
- bool busy_ = true; \
- AioWait *wait_ = (wait); \
- AioContext *ctx_ = (ctx); \
- if (in_aio_context_home_thread(ctx_)) { \
- while ((cond) || busy_) { \
- busy_ = aio_poll(ctx_, (cond)); \
- waited_ |= !!(cond) | busy_; \
- } \
- } else { \
- assert(qemu_get_current_aio_context() == \
- qemu_get_aio_context()); \
- assert(!wait_->need_kick); \
- /* Set wait_->need_kick before evaluating cond. */ \
- atomic_mb_set(&wait_->need_kick, true); \
- while (busy_) { \
- if ((cond)) { \
- waited_ = busy_ = true; \
- aio_context_release(ctx_); \
- aio_poll(qemu_get_aio_context(), true); \
- aio_context_acquire(ctx_); \
- } else { \
- busy_ = aio_poll(ctx_, false); \
- waited_ |= busy_; \
- } \
- } \
- atomic_set(&wait_->need_kick, false); \
- } \
+#define AIO_WAIT_WHILE(wait, ctx, cond) ({ \
+ bool waited_ = false; \
+ bool busy_ = true; \
+ AioWait *wait_ = (wait); \
+ AioContext *ctx_ = (ctx); \
+ if (in_aio_context_home_thread(ctx_)) { \
+ while ((cond) || busy_) { \
+ busy_ = aio_poll(ctx_, (cond)); \
+ waited_ |= !!(cond) | busy_; \
+ } \
+ } else { \
+ assert(qemu_get_current_aio_context() == \
+ qemu_get_aio_context()); \
+ /* Increment wait_->num_waiters before evaluating cond. */ \
+ atomic_inc(&wait_->num_waiters); \
+ while (busy_) { \
+ if ((cond)) { \
+ waited_ = busy_ = true; \
+ aio_context_release(ctx_); \
+ aio_poll(qemu_get_aio_context(), true); \
+ aio_context_acquire(ctx_); \
+ } else { \
+ busy_ = aio_poll(ctx_, false); \
+ waited_ |= busy_; \
+ } \
+ } \
+ atomic_dec(&wait_->num_waiters); \
+ } \
waited_; })
/**
diff --git a/util/aio-wait.c b/util/aio-wait.c
index a487cdb852..be85a32273 100644
--- a/util/aio-wait.c
+++ b/util/aio-wait.c
@@ -34,7 +34,7 @@ static void dummy_bh_cb(void *opaque)
void aio_wait_kick(AioWait *wait)
{
/* The barrier (or an atomic op) is in the caller. */
- if (atomic_read(&wait->need_kick)) {
+ if (atomic_read(&wait->num_waiters)) {
aio_bh_schedule_oneshot(qemu_get_aio_context(), dummy_bh_cb, NULL);
}
}
--
2.14.3
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [Qemu-devel] [PATCH v2] block: make BDRV_POLL_WHILE() re-entrancy safe
2018-03-07 12:46 [Qemu-devel] [PATCH v2] block: make BDRV_POLL_WHILE() re-entrancy safe Stefan Hajnoczi
@ 2018-03-07 23:19 ` Eric Blake
2018-03-12 11:07 ` [Qemu-devel] [Qemu-block] " Stefan Hajnoczi
1 sibling, 0 replies; 3+ messages in thread
From: Eric Blake @ 2018-03-07 23:19 UTC (permalink / raw)
To: Stefan Hajnoczi, qemu-devel
Cc: Kevin Wolf, Fam Zheng, qemu-block, Max Reitz, fuweiwei (C),
Paolo Bonzini
On 03/07/2018 06:46 AM, Stefan Hajnoczi wrote:
> Nested BDRV_POLL_WHILE() calls can occur. Currently
> assert(!wait_->wakeup) fails in AIO_WAIT_WHILE() when this happens.
>
> This patch converts the bool wait_->need_kick flag to an unsigned
> wait_->num_waiters counter.
>
> Nesting works correctly because outer AIO_WAIT_WHILE() callers evaluate
> the condition again after the inner caller completes (invoking the inner
> caller counts as aio_poll() progress).
>
> Reported-by: "fuweiwei (C)" <fuweiwei2@huawei.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
> v2:
> * Rebase onto qemu.git/master now that AIO_WAIT_WHILE() has landed
> [Kevin]
>
> include/block/aio-wait.h | 61 ++++++++++++++++++++++++------------------------
Looks big due to whitespace change when column for trailing \ changed.
Viewing the diff with whitespace ignored made it easier to review.
Reviewed-by: Eric Blake <eblake@redhat.com>
diff --git c/include/block/aio-wait.h w/include/block/aio-wait.h
index a48c744fa87..74cde07bef3 100644
--- c/include/block/aio-wait.h
+++ w/include/block/aio-wait.h
@@ -50,8 +50,8 @@
* }
*/
typedef struct {
- /* Is the main loop waiting for a kick? Accessed with atomic ops. */
- bool need_kick;
+ /* Number of waiting AIO_WAIT_WHILE() callers. Accessed with atomic
ops. */
+ unsigned num_waiters;
} AioWait;
/**
@@ -84,9 +84,8 @@ typedef struct {
} else { \
assert(qemu_get_current_aio_context() == \
qemu_get_aio_context()); \
- assert(!wait_->need_kick); \
- /* Set wait_->need_kick before evaluating cond. */ \
- atomic_mb_set(&wait_->need_kick, true); \
+ /* Increment wait_->num_waiters before evaluating cond. */ \
+ atomic_inc(&wait_->num_waiters); \
while (busy_) { \
if ((cond)) { \
waited_ = busy_ = true; \
@@ -98,7 +97,7 @@ typedef struct {
waited_ |= busy_; \
} \
} \
- atomic_set(&wait_->need_kick, false); \
+ atomic_dec(&wait_->num_waiters); \
} \
waited_; })
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [Qemu-devel] [Qemu-block] [PATCH v2] block: make BDRV_POLL_WHILE() re-entrancy safe
2018-03-07 12:46 [Qemu-devel] [PATCH v2] block: make BDRV_POLL_WHILE() re-entrancy safe Stefan Hajnoczi
2018-03-07 23:19 ` Eric Blake
@ 2018-03-12 11:07 ` Stefan Hajnoczi
1 sibling, 0 replies; 3+ messages in thread
From: Stefan Hajnoczi @ 2018-03-12 11:07 UTC (permalink / raw)
To: Stefan Hajnoczi
Cc: qemu-devel, Kevin Wolf, Fam Zheng, qemu-block, Max Reitz,
fuweiwei (C),
Paolo Bonzini
[-- Attachment #1: Type: text/plain, Size: 1024 bytes --]
On Wed, Mar 07, 2018 at 12:46:19PM +0000, Stefan Hajnoczi wrote:
> Nested BDRV_POLL_WHILE() calls can occur. Currently
> assert(!wait_->wakeup) fails in AIO_WAIT_WHILE() when this happens.
>
> This patch converts the bool wait_->need_kick flag to an unsigned
> wait_->num_waiters counter.
>
> Nesting works correctly because outer AIO_WAIT_WHILE() callers evaluate
> the condition again after the inner caller completes (invoking the inner
> caller counts as aio_poll() progress).
>
> Reported-by: "fuweiwei (C)" <fuweiwei2@huawei.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
> v2:
> * Rebase onto qemu.git/master now that AIO_WAIT_WHILE() has landed
> [Kevin]
>
> include/block/aio-wait.h | 61 ++++++++++++++++++++++++------------------------
> util/aio-wait.c | 2 +-
> 2 files changed, 31 insertions(+), 32 deletions(-)
Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block
Stefan
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2018-03-07 12:46 [Qemu-devel] [PATCH v2] block: make BDRV_POLL_WHILE() re-entrancy safe Stefan Hajnoczi
2018-03-07 23:19 ` Eric Blake
2018-03-12 11:07 ` [Qemu-devel] [Qemu-block] " Stefan Hajnoczi
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