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Revert "Revert "block, bfq: honor already-setup queue merges""

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[ Upstream commit 15729ff8143f8135b03988a100a19e66d7cb7ecd ]

A crash [1] happened to be triggered in conjunction with commit
2d52c58b9c9b ("block, bfq: honor already-setup queue merges"). The
latter was then reverted by commit ebc69e897e17 ("Revert "block, bfq:
honor already-setup queue merges""). Yet, the reverted commit was not
the one introducing the bug. In fact, it actually triggered a UAF
introduced by a different commit, and now fixed by commit d29bd41428cf
("block, bfq: reset last_bfqq_created on group change").

So, there is no point in keeping commit 2d52c58b9c9b ("block, bfq:
honor already-setup queue merges") out. This commit restores it.

[1] https://bugzilla.kernel.org/show_bug.cgi?id=214503

Reported-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20211125181510.15004-1-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Paolo Valente 2021-11-25 19:15:10 +01:00 committed by Greg Kroah-Hartman
parent 36b6b62b69
commit f990f0985e
1 changed files with 13 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
block/bfq-iosched.c
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@ -2155,6 +2155,15 @@ bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
* are likely to increase the throughput. * are likely to increase the throughput.
*/ */
bfqq->new_bfqq = new_bfqq; bfqq->new_bfqq = new_bfqq;
/*
* The above assignment schedules the following redirections:
* each time some I/O for bfqq arrives, the process that
* generated that I/O is disassociated from bfqq and
* associated with new_bfqq. Here we increases new_bfqq->ref
* in advance, adding the number of processes that are
* expected to be associated with new_bfqq as they happen to
* issue I/O.
*/
new_bfqq->ref += process_refs; new_bfqq->ref += process_refs;
return new_bfqq; return new_bfqq;
} }
@ -2214,6 +2223,10 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
{ {
struct bfq_queue *in_service_bfqq, *new_bfqq; struct bfq_queue *in_service_bfqq, *new_bfqq;
/* if a merge has already been setup, then proceed with that first */
if (bfqq->new_bfqq)
return bfqq->new_bfqq;
/* /*
* Prevent bfqq from being merged if it has been created too * Prevent bfqq from being merged if it has been created too
* long ago. The idea is that true cooperating processes, and * long ago. The idea is that true cooperating processes, and
@ -2228,9 +2241,6 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
if (bfq_too_late_for_merging(bfqq)) if (bfq_too_late_for_merging(bfqq))
return NULL; return NULL;
if (bfqq->new_bfqq)
return bfqq->new_bfqq;
if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq)) if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq))
return NULL; return NULL;