On Wed, 4 Sep 2024 12:56:33 -0700 Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> On 9/4/24 12:26, Liam R. Howlett wrote:
> > * Guenter Roeck <linux@xxxxxxxxxxxx> [240904 00:27]:
> >> On 9/3/24 20:36, Liam R. Howlett wrote:
> >>> * Guenter Roeck <linux@xxxxxxxxxxxx> [240903 22:38]:
> >>>> On 9/3/24 19:31, Liam R. Howlett wrote:
> >>>>> * SeongJae Park <sj@xxxxxxxxxx> [240903 21:18]:
> >>>>>> On Tue, 3 Sep 2024 17:58:15 -0700 SeongJae Park <sj@xxxxxxxxxx> wrote:
> >>>>>>
> >>>>>>> On Tue, 3 Sep 2024 20:48:53 -0400 "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx> wrote:
> >>>>>>>
> >>>>>>>> * SeongJae Park <sj@xxxxxxxxxx> [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@xxxxxxxxxx
Thanks,
SJ
>
> Thanks,
> Guenter
