Message ID | 20150122085254.5276.53380.stgit@PASHA-ISP.def.inno |
---|---|
State | New |
Headers | show |
On 22/01/2015 09:52, Pavel Dovgalyuk wrote: > Bottom halves in AIO context are stored and removes > in LIFO order. It makes their execution non-deterministic. > This patch replaces the stack with queue to preserve the > order of bottom halves processing. > > Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru> > --- > async.c | 25 +++++++++---------------- > include/block/aio.h | 4 ++-- > include/qemu/queue.h | 7 +++++++ > 3 files changed, 18 insertions(+), 18 deletions(-) > > diff --git a/async.c b/async.c > index 2be88cc..bc6e83b 100644 > --- a/async.c > +++ b/async.c > @@ -35,7 +35,7 @@ struct QEMUBH { > AioContext *ctx; > QEMUBHFunc *cb; > void *opaque; > - QEMUBH *next; > + QSIMPLEQ_ENTRY(QEMUBH) next; > bool scheduled; > bool idle; > bool deleted; > @@ -51,10 +51,7 @@ QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque) > .opaque = opaque, > }; > qemu_mutex_lock(&ctx->bh_lock); > - bh->next = ctx->first_bh; > - /* Make sure that the members are ready before putting bh into list */ > - smp_wmb(); > - ctx->first_bh = bh; > + QSIMPLEQ_INSERT_TAIL_RCU(&ctx->bh_queue, bh, next); > qemu_mutex_unlock(&ctx->bh_lock); > return bh; > } > @@ -62,16 +59,15 @@ QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque) > /* Multiple occurrences of aio_bh_poll cannot be called concurrently */ > int aio_bh_poll(AioContext *ctx) > { > - QEMUBH *bh, **bhp, *next; > + QEMUBH *bh, *next; > int ret; > > ctx->walking_bh++; > > ret = 0; > - for (bh = ctx->first_bh; bh; bh = next) { > + QSIMPLEQ_FOREACH_SAFE(bh, &ctx->bh_queue, next, next) { > /* Make sure that fetching bh happens before accessing its members */ > smp_read_barrier_depends(); > - next = bh->next; Must use QSIMPLEQ_FOREACH. Otherwise, the access of next is before the smp_read_barrier_depends(). > if (!bh->deleted && bh->scheduled) { > bh->scheduled = 0; > /* Paired with write barrier in bh schedule to ensure reading for > @@ -90,14 +86,10 @@ int aio_bh_poll(AioContext *ctx) > /* remove deleted bhs */ > if (!ctx->walking_bh) { > qemu_mutex_lock(&ctx->bh_lock); > - bhp = &ctx->first_bh; > - while (*bhp) { > - bh = *bhp; > + QSIMPLEQ_FOREACH_SAFE(bh, &ctx->bh_queue, next, next) { > if (bh->deleted) { > - *bhp = bh->next; > + QSIMPLEQ_REMOVE(&ctx->bh_queue, bh, QEMUBH, next); > g_free(bh); > - } else { > - bhp = &bh->next; > } > } > qemu_mutex_unlock(&ctx->bh_lock); > @@ -161,7 +153,7 @@ aio_compute_timeout(AioContext *ctx) > int timeout = -1; > QEMUBH *bh; > > - for (bh = ctx->first_bh; bh; bh = bh->next) { > + QSIMPLEQ_FOREACH(bh, &ctx->bh_queue, next) { > if (!bh->deleted && bh->scheduled) { > if (bh->idle) { > /* idle bottom halves will be polled at least > @@ -204,7 +196,7 @@ aio_ctx_check(GSource *source) > AioContext *ctx = (AioContext *) source; > QEMUBH *bh; > > - for (bh = ctx->first_bh; bh; bh = bh->next) { > + QSIMPLEQ_FOREACH(bh, &ctx->bh_queue, next) { > if (!bh->deleted && bh->scheduled) { > return true; > } > @@ -311,6 +303,7 @@ AioContext *aio_context_new(Error **errp) > qemu_mutex_init(&ctx->bh_lock); > rfifolock_init(&ctx->lock, aio_rfifolock_cb, ctx); > timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx); > + QSIMPLEQ_INIT(&ctx->bh_queue); > > return ctx; > } > diff --git a/include/block/aio.h b/include/block/aio.h > index 7d1e26b..82cdf78 100644 > --- a/include/block/aio.h > +++ b/include/block/aio.h > @@ -71,8 +71,8 @@ struct AioContext { > /* lock to protect between bh's adders and deleter */ > QemuMutex bh_lock; > > - /* Anchor of the list of Bottom Halves belonging to the context */ > - struct QEMUBH *first_bh; > + /* List of Bottom Halves belonging to the context */ > + QSIMPLEQ_HEAD(, QEMUBH) bh_queue; > > /* A simple lock used to protect the first_bh list, and ensure that > * no callbacks are removed while we're walking and dispatching callbacks. > diff --git a/include/qemu/queue.h b/include/qemu/queue.h > index a98eb3a..b94c4d4 100644 > --- a/include/qemu/queue.h > +++ b/include/qemu/queue.h > @@ -268,6 +268,13 @@ struct { \ > (head)->sqh_last = &(elm)->field.sqe_next; \ > } while (/*CONSTCOND*/0) > > +#define QSIMPLEQ_INSERT_TAIL_RCU(head, elm, field) do { \ > + (elm)->field.sqe_next = NULL; \ > + *(head)->sqh_last = (elm); \ > + (head)->sqh_last = &(elm)->field.sqe_next; \ > + smp_wmb(); \ smp_wmb() must be after the (elm) assignment. Paolo > +} while (/*CONSTCOND*/0) > + > #define QSIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do { \ > if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL) \ > (head)->sqh_last = &(elm)->field.sqe_next; \ >
diff --git a/async.c b/async.c index 2be88cc..bc6e83b 100644 --- a/async.c +++ b/async.c @@ -35,7 +35,7 @@ struct QEMUBH { AioContext *ctx; QEMUBHFunc *cb; void *opaque; - QEMUBH *next; + QSIMPLEQ_ENTRY(QEMUBH) next; bool scheduled; bool idle; bool deleted; @@ -51,10 +51,7 @@ QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque) .opaque = opaque, }; qemu_mutex_lock(&ctx->bh_lock); - bh->next = ctx->first_bh; - /* Make sure that the members are ready before putting bh into list */ - smp_wmb(); - ctx->first_bh = bh; + QSIMPLEQ_INSERT_TAIL_RCU(&ctx->bh_queue, bh, next); qemu_mutex_unlock(&ctx->bh_lock); return bh; } @@ -62,16 +59,15 @@ QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque) /* Multiple occurrences of aio_bh_poll cannot be called concurrently */ int aio_bh_poll(AioContext *ctx) { - QEMUBH *bh, **bhp, *next; + QEMUBH *bh, *next; int ret; ctx->walking_bh++; ret = 0; - for (bh = ctx->first_bh; bh; bh = next) { + QSIMPLEQ_FOREACH_SAFE(bh, &ctx->bh_queue, next, next) { /* Make sure that fetching bh happens before accessing its members */ smp_read_barrier_depends(); - next = bh->next; if (!bh->deleted && bh->scheduled) { bh->scheduled = 0; /* Paired with write barrier in bh schedule to ensure reading for @@ -90,14 +86,10 @@ int aio_bh_poll(AioContext *ctx) /* remove deleted bhs */ if (!ctx->walking_bh) { qemu_mutex_lock(&ctx->bh_lock); - bhp = &ctx->first_bh; - while (*bhp) { - bh = *bhp; + QSIMPLEQ_FOREACH_SAFE(bh, &ctx->bh_queue, next, next) { if (bh->deleted) { - *bhp = bh->next; + QSIMPLEQ_REMOVE(&ctx->bh_queue, bh, QEMUBH, next); g_free(bh); - } else { - bhp = &bh->next; } } qemu_mutex_unlock(&ctx->bh_lock); @@ -161,7 +153,7 @@ aio_compute_timeout(AioContext *ctx) int timeout = -1; QEMUBH *bh; - for (bh = ctx->first_bh; bh; bh = bh->next) { + QSIMPLEQ_FOREACH(bh, &ctx->bh_queue, next) { if (!bh->deleted && bh->scheduled) { if (bh->idle) { /* idle bottom halves will be polled at least @@ -204,7 +196,7 @@ aio_ctx_check(GSource *source) AioContext *ctx = (AioContext *) source; QEMUBH *bh; - for (bh = ctx->first_bh; bh; bh = bh->next) { + QSIMPLEQ_FOREACH(bh, &ctx->bh_queue, next) { if (!bh->deleted && bh->scheduled) { return true; } @@ -311,6 +303,7 @@ AioContext *aio_context_new(Error **errp) qemu_mutex_init(&ctx->bh_lock); rfifolock_init(&ctx->lock, aio_rfifolock_cb, ctx); timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx); + QSIMPLEQ_INIT(&ctx->bh_queue); return ctx; } diff --git a/include/block/aio.h b/include/block/aio.h index 7d1e26b..82cdf78 100644 --- a/include/block/aio.h +++ b/include/block/aio.h @@ -71,8 +71,8 @@ struct AioContext { /* lock to protect between bh's adders and deleter */ QemuMutex bh_lock; - /* Anchor of the list of Bottom Halves belonging to the context */ - struct QEMUBH *first_bh; + /* List of Bottom Halves belonging to the context */ + QSIMPLEQ_HEAD(, QEMUBH) bh_queue; /* A simple lock used to protect the first_bh list, and ensure that * no callbacks are removed while we're walking and dispatching callbacks. diff --git a/include/qemu/queue.h b/include/qemu/queue.h index a98eb3a..b94c4d4 100644 --- a/include/qemu/queue.h +++ b/include/qemu/queue.h @@ -268,6 +268,13 @@ struct { \ (head)->sqh_last = &(elm)->field.sqe_next; \ } while (/*CONSTCOND*/0) +#define QSIMPLEQ_INSERT_TAIL_RCU(head, elm, field) do { \ + (elm)->field.sqe_next = NULL; \ + *(head)->sqh_last = (elm); \ + (head)->sqh_last = &(elm)->field.sqe_next; \ + smp_wmb(); \ +} while (/*CONSTCOND*/0) + #define QSIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do { \ if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL) \ (head)->sqh_last = &(elm)->field.sqe_next; \
Bottom halves in AIO context are stored and removes in LIFO order. It makes their execution non-deterministic. This patch replaces the stack with queue to preserve the order of bottom halves processing. Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru> --- async.c | 25 +++++++++---------------- include/block/aio.h | 4 ++-- include/qemu/queue.h | 7 +++++++ 3 files changed, 18 insertions(+), 18 deletions(-)