diff options
author | Alberto Garcia <berto@igalia.com> | 2016-10-17 18:46:02 +0300 |
---|---|---|
committer | Michael Roth <mdroth@linux.vnet.ibm.com> | 2016-11-02 18:19:00 -0500 |
commit | b1fdc9419322247fd7faaa8e795fa80176825459 (patch) | |
tree | 4cf4b87dc73a3785a586309d2b69585e3bf44d99 | |
parent | 61781984dbadc2ed7af51e1f818a7d8beec2ec7b (diff) | |
download | qemu-b1fdc9419322247fd7faaa8e795fa80176825459.tar.gz |
throttle: Correct access to wrong BlockBackendPublic structures
In 27ccdd52598290f0f8b58be56e235aff7aebfaf3 the throttling fields were
moved from BlockDriverState to BlockBackend. However in a few cases
the code started using throttling fields from the active BlockBackend
instead of the round-robin token, making the algorithm behave
incorrectly.
This can cause starvation if there's a throttling group with several
drives but only one of them has I/O.
Cc: qemu-stable@nongnu.org
Reported-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit 6bf77e1c2dc24da1bade16e8a9a637f3b127314d)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
-rw-r--r-- | block/throttle-groups.c | 27 |
1 files changed, 23 insertions, 4 deletions
diff --git a/block/throttle-groups.c b/block/throttle-groups.c index 59545e287e..17b2efb7c7 100644 --- a/block/throttle-groups.c +++ b/block/throttle-groups.c @@ -168,6 +168,22 @@ static BlockBackend *throttle_group_next_blk(BlockBackend *blk) return blk_by_public(next); } +/* + * Return whether a BlockBackend has pending requests. + * + * This assumes that tg->lock is held. + * + * @blk: the BlockBackend + * @is_write: the type of operation (read/write) + * @ret: whether the BlockBackend has pending requests. + */ +static inline bool blk_has_pending_reqs(BlockBackend *blk, + bool is_write) +{ + const BlockBackendPublic *blkp = blk_get_public(blk); + return blkp->pending_reqs[is_write]; +} + /* Return the next BlockBackend in the round-robin sequence with pending I/O * requests. * @@ -188,7 +204,7 @@ static BlockBackend *next_throttle_token(BlockBackend *blk, bool is_write) /* get next bs round in round robin style */ token = throttle_group_next_blk(token); - while (token != start && !blkp->pending_reqs[is_write]) { + while (token != start && !blk_has_pending_reqs(token, is_write)) { token = throttle_group_next_blk(token); } @@ -196,10 +212,13 @@ static BlockBackend *next_throttle_token(BlockBackend *blk, bool is_write) * then decide the token is the current bs because chances are * the current bs get the current request queued. */ - if (token == start && !blkp->pending_reqs[is_write]) { + if (token == start && !blk_has_pending_reqs(token, is_write)) { token = blk; } + /* Either we return the original BB, or one with pending requests */ + assert(token == blk || blk_has_pending_reqs(token, is_write)); + return token; } @@ -257,7 +276,7 @@ static void schedule_next_request(BlockBackend *blk, bool is_write) /* Check if there's any pending request to schedule next */ token = next_throttle_token(blk, is_write); - if (!blkp->pending_reqs[is_write]) { + if (!blk_has_pending_reqs(token, is_write)) { return; } @@ -271,7 +290,7 @@ static void schedule_next_request(BlockBackend *blk, bool is_write) qemu_co_queue_next(&blkp->throttled_reqs[is_write])) { token = blk; } else { - ThrottleTimers *tt = &blkp->throttle_timers; + ThrottleTimers *tt = &blk_get_public(token)->throttle_timers; int64_t now = qemu_clock_get_ns(tt->clock_type); timer_mod(tt->timers[is_write], now + 1); tg->any_timer_armed[is_write] = true; |