On Wed, 4 Sep 2024 12:56:33 -0700 Guenter Roeck linux@roeck-us.net wrote:
On 9/4/24 12:26, Liam R. Howlett wrote:
- Guenter Roeck linux@roeck-us.net [240904 00:27]:
On 9/3/24 20:36, Liam R. Howlett wrote:
- Guenter Roeck linux@roeck-us.net [240903 22:38]:
On 9/3/24 19:31, Liam R. Howlett wrote:
- SeongJae Park sj@kernel.org [240903 21:18]:
> On Tue, 3 Sep 2024 17:58:15 -0700 SeongJae Park sj@kernel.org wrote: > >> On Tue, 3 Sep 2024 20:48:53 -0400 "Liam R. Howlett" Liam.Howlett@oracle.com wrote: >> >>> * SeongJae Park sj@kernel.org [240903 20:45]:
[...]
I am running ./tools/testing/kunit/kunit.py run '*damon*' --arch x86_64 --raw with: CONFIG_LOCKDEP=y CONFIG_DEBUG_SPINLOCK=y
and I don't have any issue with locking in the existing code. How do I recreate this issue?
I tested again, and I still see
[ 6.233483] ok 4 damon [ 6.234190] KTAP version 1 [ 6.234263] # Subtest: damon-operations [ 6.234335] # module: vaddr [ 6.234384] 1..6 [ 6.235726] [ 6.235931] ============================= [ 6.236018] WARNING: suspicious RCU usage [ 6.236280] 6.11.0-rc6-00029-gda66250b210f-dirty #1 Tainted: G N [ 6.236398] ----------------------------- [ 6.236474] lib/maple_tree.c:832 suspicious rcu_dereference_check() usage! [ 6.236579] [ 6.236579] other info that might help us debug this: [ 6.236579] [ 6.236738] [ 6.236738] rcu_scheduler_active = 2, debug_locks = 1 [ 6.237039] no locks held by kunit_try_catch/208. [ 6.237166] [ 6.237166] stack backtrace: [ 6.237385] CPU: 0 UID: 0 PID: 208 Comm: kunit_try_catch Tainted: G N 6.11.0-rc6-00029-gda66250b210f-dirty #1 [ 6.237629] Tainted: [N]=TEST [ 6.237714] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 [ 6.238065] Call Trace: [ 6.238233] <TASK> [ 6.238547] dump_stack_lvl+0x9e/0xe0 [ 6.239473] lockdep_rcu_suspicious+0x145/0x1b0 [ 6.239621] mas_walk+0x19f/0x1d0 [ 6.239765] mas_find+0xb5/0x150 [ 6.239873] __damon_va_three_regions+0x7e/0x130
I was able to reproduce this by further enabling PROVE_LOCKING.
This function isn't taking the rcu read lock while iterating the tree.
Try this:
diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c index b0e8b361891d..08cfd22b5249 100644 --- a/mm/damon/vaddr.c +++ b/mm/damon/vaddr.c @@ -126,6 +126,7 @@ static int __damon_va_three_regions(struct mm_struct *mm, * If this is too slow, it can be optimised to examine the maple * tree gaps. */
rcu_read_lock(); for_each_vma(vmi, vma) { unsigned long gap;@@ -146,6 +147,7 @@ static int __damon_va_three_regions(struct mm_struct *mm, next: prev = vma; }
rcu_read_unlock();if (!sz_range(&second_gap) || !sz_range(&first_gap)) return -EINVAL;
Yes, that fixes the problem for me.
Thank you for the fix, Liam. Thank you for the test, Guenter. I also confirmed this fix works on my setup.
I posted the fix as a formal patch: https://lore.kernel.org/20240905001204.1481-1-sj@kernel.org
Thanks, SJ
Thanks, Guenter