From e8a095dadb70e2ea6d5169d261920db3747bfa45 Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Thu, 16 Jun 2016 17:56:26 +0100 Subject: [PATCH] block: use safe iteration over AioContext notifiers It's possible that an AioContext notifier user was close to finishing when .detach_aio_context() or .attached_aio_context() is called. In that case they may call bdrv_remove_aio_context_notifier() during the callback. Use safe iteration to avoid crashing when the notifier list is modified during iteration. We must not only handle the case where the current aio notifier is removed during a callback but also the one where any other aio notifier is removed. The next patch adds an AioContext notifier for block jobs and they really could be terminating just as .detach_aio_context() is invoked. Signed-off-by: Stefan Hajnoczi Reviewed-by: Paolo Bonzini Reviewed-by: Fam Zheng Message-id: 1466096189-6477-6-git-send-email-stefanha@redhat.com --- block.c | 46 ++++++++++++++++++++++++++++++++++++---------- include/block/block_int.h | 2 ++ 2 files changed, 38 insertions(+), 10 deletions(-) diff --git a/block.c b/block.c index b331eb9..c0ccc27 100644 --- a/block.c +++ b/block.c @@ -3609,18 +3609,34 @@ AioContext *bdrv_get_aio_context(BlockDriverState *bs) return bs->aio_context; } +static void bdrv_do_remove_aio_context_notifier(BdrvAioNotifier *ban) +{ + QLIST_REMOVE(ban, list); + g_free(ban); +} + void bdrv_detach_aio_context(BlockDriverState *bs) { - BdrvAioNotifier *baf; + BdrvAioNotifier *baf, *baf_tmp; BdrvChild *child; if (!bs->drv) { return; } - QLIST_FOREACH(baf, &bs->aio_notifiers, list) { - baf->detach_aio_context(baf->opaque); + assert(!bs->walking_aio_notifiers); + bs->walking_aio_notifiers = true; + QLIST_FOREACH_SAFE(baf, &bs->aio_notifiers, list, baf_tmp) { + if (baf->deleted) { + bdrv_do_remove_aio_context_notifier(baf); + } else { + baf->detach_aio_context(baf->opaque); + } } + /* Never mind iterating again to check for ->deleted. bdrv_close() will + * remove remaining aio notifiers if we aren't called again. + */ + bs->walking_aio_notifiers = false; if (bs->drv->bdrv_detach_aio_context) { bs->drv->bdrv_detach_aio_context(bs); @@ -3635,7 +3651,7 @@ void bdrv_detach_aio_context(BlockDriverState *bs) void bdrv_attach_aio_context(BlockDriverState *bs, AioContext *new_context) { - BdrvAioNotifier *ban; + BdrvAioNotifier *ban, *ban_tmp; BdrvChild *child; if (!bs->drv) { @@ -3651,9 +3667,16 @@ void bdrv_attach_aio_context(BlockDriverState *bs, bs->drv->bdrv_attach_aio_context(bs, new_context); } - QLIST_FOREACH(ban, &bs->aio_notifiers, list) { - ban->attached_aio_context(new_context, ban->opaque); + assert(!bs->walking_aio_notifiers); + bs->walking_aio_notifiers = true; + QLIST_FOREACH_SAFE(ban, &bs->aio_notifiers, list, ban_tmp) { + if (ban->deleted) { + bdrv_do_remove_aio_context_notifier(ban); + } else { + ban->attached_aio_context(new_context, ban->opaque); + } } + bs->walking_aio_notifiers = false; } void bdrv_set_aio_context(BlockDriverState *bs, AioContext *new_context) @@ -3695,11 +3718,14 @@ void bdrv_remove_aio_context_notifier(BlockDriverState *bs, QLIST_FOREACH_SAFE(ban, &bs->aio_notifiers, list, ban_next) { if (ban->attached_aio_context == attached_aio_context && ban->detach_aio_context == detach_aio_context && - ban->opaque == opaque) + ban->opaque == opaque && + ban->deleted == false) { - QLIST_REMOVE(ban, list); - g_free(ban); - + if (bs->walking_aio_notifiers) { + ban->deleted = true; + } else { + bdrv_do_remove_aio_context_notifier(ban); + } return; } } diff --git a/include/block/block_int.h b/include/block/block_int.h index 688c6be..2057156 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -361,6 +361,7 @@ typedef struct BdrvAioNotifier { void (*detach_aio_context)(void *opaque); void *opaque; + bool deleted; QLIST_ENTRY(BdrvAioNotifier) list; } BdrvAioNotifier; @@ -427,6 +428,7 @@ struct BlockDriverState { * BDS may register themselves in this list to be notified of changes * regarding this BDS's context */ QLIST_HEAD(, BdrvAioNotifier) aio_notifiers; + bool walking_aio_notifiers; /* to make removal during iteration safe */ char filename[PATH_MAX]; char backing_file[PATH_MAX]; /* if non zero, the image is a diff of -- 2.7.4