Tejun Heo a7c8067453 iocost: Fix divide-by-zero on donation from low hweight cgroup ... commit edaa26334c117a584add6053f48d63a988d25a6e upstream. The donation calculation logic assumes that the donor has non-zero after-donation hweight, so the lowest active hweight a donating cgroup can have is 2 so that it can donate 1 while keeping the other 1 for itself. Earlier, we only donated from cgroups with sizable surpluses so this condition was always true. However, with the precise donation algorithm implemented, f1de2439ec ("blk-iocost: revamp donation amount determination") made the donation amount calculation exact enabling even low hweight cgroups to donate. This means that in rare occasions, a cgroup with active hweight of 1 can enter donation calculation triggering the following warning and then a divide-by-zero oops. WARNING: CPU: 4 PID: 0 at block/blk-iocost.c:1928 transfer_surpluses.cold+0x0/0x53 [884/94867] ... RIP: 0010:transfer_surpluses.cold+0x0/0x53 Code: 92 ff 48 c7 c7 28 d1 ab b5 65 48 8b 34 25 00 ae 01 00 48 81 c6 90 06 00 00 e8 8b 3f fe ff 48 c7 c0 ea ff ff ff e9 95 ff 92 ff <0f> 0b 48 c7 c7 30 da ab b5 e8 71 3f fe ff 4c 89 e8 4d 85 ed 74 0 4 ... Call Trace: <IRQ> ioc_timer_fn+0x1043/0x1390 call_timer_fn+0xa1/0x2c0 __run_timers.part.0+0x1ec/0x2e0 run_timer_softirq+0x35/0x70 ... iocg: invalid donation weights in /a/b: active=1 donating=1 after=0 Fix it by excluding cgroups w/ active hweight < 2 from donating. Excluding these extreme low hweight donations shouldn't affect work conservation in any meaningful way. Signed-off-by: Tejun Heo <tj@kernel.org> Fixes: f1de2439ec ("blk-iocost: revamp donation amount determination") Cc: stable@vger.kernel.org # v5.10+ Link: https://lore.kernel.org/r/Ybfh86iSvpWKxhVM@slm.duckdns.org Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2021-12-22 09:30:57 +01:00
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partitions
badblocks.c
bfq-cgroup.c
bfq-iosched.c
bfq-iosched.h
bfq-wf2q.c
bio-integrity.c
bio.c
blk-cgroup-rwstat.c
blk-cgroup-rwstat.h
blk-cgroup.c
blk-core.c
blk-crypto-fallback.c
blk-crypto-internal.h
blk-crypto.c
blk-exec.c
blk-flush.c
blk-integrity.c
blk-ioc.c
blk-iocost.c
blk-iolatency.c
blk-lib.c
blk-map.c
blk-merge.c
blk-mq-cpumap.c
blk-mq-debugfs-zoned.c
blk-mq-debugfs.c
blk-mq-debugfs.h
blk-mq-pci.c
blk-mq-rdma.c
blk-mq-sched.c
blk-mq-sched.h
blk-mq-sysfs.c
blk-mq-tag.c
blk-mq-tag.h
blk-mq-virtio.c
blk-mq.c
blk-mq.h
blk-pm.c
blk-pm.h
blk-rq-qos.c
blk-rq-qos.h
blk-settings.c
blk-stat.c
blk-stat.h
blk-sysfs.c
blk-throttle.c
blk-timeout.c
blk-wbt.c
blk-wbt.h
blk-zoned.c
blk.h
bounce.c
bsg-lib.c
bsg.c
cmdline-parser.c
elevator.c
genhd.c
ioctl.c
ioprio.c
Kconfig
Kconfig.iosched
keyslot-manager.c
kyber-iosched.c
Makefile
mq-deadline.c
opal_proto.h
scsi_ioctl.c
sed-opal.c
t10-pi.c