On 11/14/19 10:33 AM, Paolo Valente wrote:
Since commit 3726112ec731 ("block, bfq: re-schedule empty queues if
they deserve I/O plugging"), to prevent the service guarantees of a
bfq_queue from being violated, the bfq_queue may be left busy, i.e.,
scheduled for service, even if empty (see comments in
__bfq_bfqq_expire() for details). But, if no process will send
requests to the bfq_queue any longer, then there is no point in
keeping the bfq_queue scheduled for service.
In addition, keeping the bfq_queue scheduled for service, but with no
process reference any longer, may cause the bfq_queue to be freed when
descheduled from service. But this is assumed to never happen, and
causes a UAF if it happens. This, in turn, caused crashes [1, 2].
This commit fixes this issue by descheduling an empty bfq_queue when
it remains with not process reference.
[1] https://bugzilla.redhat.com/show_bug.cgi?id=1767539
[2] https://bugzilla.kernel.org/show_bug.cgi?id=205447
Fixes: 3726112ec731 ("block, bfq: re-schedule empty queues if they deserve I/O plugging")
Reported-by: Chris Evich <cevich@xxxxxxxxxx>
Reported-by: Patrick Dung <patdung100@xxxxxxxxx>
Reported-by: Thorsten Schubert <tschubert@xxxxxxxx>
Tested-by: Thorsten Schubert <tschubert@xxxxxxxx>
Tested-by: Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx>
Signed-off-by: Paolo Valente <paolo.valente@xxxxxxxxxx>
Jens,
can you please also tag this for stable-5.3 before the next push?
The original problem was found on 5.3 after all, and hoping for the
stable-bot to pick it up automagically is a bit unreliable.
Thanks,
Holger
