aboutsummaryrefslogtreecommitdiff
path: root/block
diff options
context:
space:
mode:
authorAlberto Garcia <berto@igalia.com>2016-10-17 18:46:02 +0300
committerKevin Wolf <kwolf@redhat.com>2016-10-24 17:54:03 +0200
commit6bf77e1c2dc24da1bade16e8a9a637f3b127314d (patch)
treeac77620a874cf822efda48467f8d2d558a72074f /block
parent3ac2f2f765a0bc18dfb18c38a522e6123289ffc1 (diff)
downloadqemu-6bf77e1c2dc24da1bade16e8a9a637f3b127314d.zip
qemu-6bf77e1c2dc24da1bade16e8a9a637f3b127314d.tar.gz
qemu-6bf77e1c2dc24da1bade16e8a9a637f3b127314d.tar.bz2
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>
Diffstat (limited to 'block')
-rw-r--r--block/throttle-groups.c27
1 files changed, 23 insertions, 4 deletions
diff --git a/block/throttle-groups.c b/block/throttle-groups.c
index 59545e2..17b2efb 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;