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Joan Bruguera Micó 26e239b37e mm: shrinkers: fix race condition on debugfs cleanup 
When something registers and unregisters many shrinkers, such as:
    for x in $(seq 10000); do unshare -Ui true; done

Sometimes the following error is printed to the kernel log:
    debugfs: Directory '...' with parent 'shrinker' already present!

This occurs since commit badc28d492 ("mm: shrinkers: fix deadlock in
shrinker debugfs") / v6.2: Since the call to `debugfs_remove_recursive`
was moved outside the `shrinker_rwsem`/`shrinker_mutex` lock, but the call
to `ida_free` stayed inside, a newly registered shrinker can be
re-assigned that ID and attempt to create the debugfs directory before the
directory from the previous shrinker has been removed.

The locking changes in commit f95bdb700b ("mm: vmscan: make global slab
shrink lockless") made the race condition more likely, though it existed
before then.

Commit badc28d492 ("mm: shrinkers: fix deadlock in shrinker debugfs")
could be reverted since the issue is addressed should no longer occur
since the count and scan operations are lockless since commit 20cd1892fc
("mm: shrinkers: make count and scan in shrinker debugfs lockless"). 
However, since this is a contended lock, prefer instead moving `ida_free`
outside the lock to avoid the race.

Link: https://lkml.kernel.org/r/20230503013232.299211-1-joanbrugueram@gmail.com
Fixes: badc28d492 ("mm: shrinkers: fix deadlock in shrinker debugfs")
Signed-off-by: Joan Bruguera Micó <joanbrugueram@gmail.com>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-05-17 15:24:33 -07:00
..
acpi Power management updates for 6.4-rc1 2023-04-25 18:44:10 -07:00
asm-generic Locking changes in v6.4: 2023-05-05 12:56:55 -07:00
clocksource KVM: arm64: timers: Use CNTPOFF_EL2 to offset the physical timer 2023-03-30 19:01:09 +01:00
crypto This update includes the following changes: 2023-04-26 08:32:52 -07:00
drm - Nick Piggin's "shoot lazy tlbs" series, to improve the peformance of 2023-04-27 19:42:02 -07:00
dt-bindings - mailbox api: allow direct registration to a channel 2023-05-07 10:17:33 -07:00
keys
kunit kunit: increase KUNIT_LOG_SIZE to 2048 bytes 2023-03-29 18:55:41 -06:00
kvm s390: 2023-05-01 12:06:20 -07:00
linux mm: shrinkers: fix race condition on debugfs cleanup 2023-05-17 15:24:33 -07:00
math-emu
media media: i2c: Drop unused sr030pc30 camera sensor driver 2023-04-15 09:56:49 +01:00
memory
misc
net Including fixes from netfilter. 2023-05-05 19:12:01 -07:00
pcmcia
ras
rdma RDMA: Add ib_virt_dma_to_page() 2023-04-16 11:08:07 +03:00
rv
scsi Driver core changes for 6.4-rc1 2023-04-27 11:53:57 -07:00
soc Nothing looks out of the ordinary in this batch of clk driver updates. There 2023-04-29 17:29:39 -07:00
sound ASoC: Updates for v6.4 2023-04-24 15:15:31 +02:00
target
trace NFSD 6.4 Release Notes 2023-04-29 11:04:14 -07:00
uapi for-6.4/block-2023-05-06 2023-05-06 08:28:58 -07:00
ufs SCSI misc on 20230426 2023-04-26 15:39:25 -07:00
vdso
video
xen