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throttle: Correct access to wrong BlockBackendPublic structures

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In 27ccdd5259 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>
This commit is contained in:
Alberto Garcia 2016-10-17 18:46:02 +03:00 committed by Kevin Wolf
parent 3ac2f2f765
commit 6bf77e1c2d
1 changed files with 23 additions and 4 deletions
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27
block/throttle-groups.c
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@ -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;