On Tue, 3 Sep 2024 20:48:53 -0400 "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx> wrote: > * SeongJae Park <sj@xxxxxxxxxx> [240903 20:45]: > > damon_test_three_regions_in_vmas() initializes a maple tree with > > MM_MT_FLAGS. The flags contains MT_FLAGS_LOCK_EXTERN, which means > > mt_lock of the maple tree will not be used. And therefore the maple > > tree initialization code skips initialization of the mt_lock. However, > > __link_vmas(), which adds vmas for test to the maple tree, uses the > > mt_lock. In other words, the uninitialized spinlock is used. The > > problem becomes celar when spinlock debugging is turned on, since it > > reports spinlock bad magic bug. Fix the issue by not using the mt_lock > > as promised. > > You can't do this, lockdep will tell you this is wrong. Hmm, but lockdep was silence on my setup? > We need a lock and to use the lock for writes. This code is executed by a single-thread test code. Do we still need the lock? > > I'd suggest using different flags so the spinlock is used. The reporter mentioned simply dropping MT_FLAGS_LOCK_EXTERN from the flags causes suspicious RCU usage message. May I ask if you have a suggestion of better flags? Thanks, SJ > > > > > Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx> > > Closes: https://lore.kernel.org/1453b2b2-6119-4082-ad9e-f3c5239bf87e@xxxxxxxxxxxx > > Fixes: d0cf3dd47f0d ("damon: convert __damon_va_three_regions to use the VMA iterator") > > Signed-off-by: SeongJae Park <sj@xxxxxxxxxx> > > --- > > mm/damon/tests/vaddr-kunit.h | 10 +++------- > > 1 file changed, 3 insertions(+), 7 deletions(-) > > > > diff --git a/mm/damon/tests/vaddr-kunit.h b/mm/damon/tests/vaddr-kunit.h > > index 83626483f82b..c6c7e0e0ab07 100644 > > --- a/mm/damon/tests/vaddr-kunit.h > > +++ b/mm/damon/tests/vaddr-kunit.h > > @@ -17,23 +17,19 @@ > > static int __link_vmas(struct maple_tree *mt, struct vm_area_struct *vmas, > > ssize_t nr_vmas) > > { > > - int i, ret = -ENOMEM; > > + int i; > > MA_STATE(mas, mt, 0, 0); > > > > if (!nr_vmas) > > return 0; > > > > - mas_lock(&mas); > > for (i = 0; i < nr_vmas; i++) { > > mas_set_range(&mas, vmas[i].vm_start, vmas[i].vm_end - 1); > > if (mas_store_gfp(&mas, &vmas[i], GFP_KERNEL)) > > - goto failed; > > + return -ENOMEM; > > } > > > > - ret = 0; > > -failed: > > - mas_unlock(&mas); > > - return ret; > > + return 0; > > } > > > > /* > > -- > > 2.39.2 > >
