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Howlett" Cc: SeongJae Park , Andrew Morton , "Matthew Wilcox (Oracle)" , David Hildenbrand , Brendan Higgins , David Gow , damon@lists.linux.dev, linux-mm@kvack.org, kunit-dev@googlegroups.com, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Guenter Roeck Subject: Re: [PATCH] mm/damon/tests/vaddr-kunit: don't use mas_lock for MM_MT_FLAGS-initialized maple tree Date: Tue, 3 Sep 2024 17:58:15 -0700 Message-Id: <20240904005815.1388-1-sj@kernel.org> X-Mailer: git-send-email 2.39.2 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: CE5CA1A0005 X-Rspamd-Server: rspam01 X-Stat-Signature: 7iuybza7oxiegs8qgiu1o694kinmrajc X-HE-Tag: 1725411500-181771 X-HE-Meta: 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 WGdZDX4c FqQP2hP0TdzDRd8E84getHvCux8o2arf5x+m0Tku/g1Fg3jM/gRHQ0wWmsZABRAcJD7+HsppUVOZwGv86xXb4hGLXaP2qmX3iHQoEhii7iP60pAImyDk02ou5o5+jMyIPTFvGoPPUyse2ohjfLLbEctkRGdvZOf6jZrw33PN3tsHQ+tPAvWRvlO03x8CWsfsEKFFhzGMpAso+KRURLoOLcwJukMYOcvsFHY+mUgAZP4eXs2dx+lpeTGVbgp7jQmuAm0ScMD3GnJCdqPj0+vpOnP2mvrbNUtGHfE00rRJ/oNYhnRegTJzKYeg9j2R4s+dpNYJjFbLAdG75+nvQVl+0jKyXmxBOTIUn2EBefLNxL8iec/w= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 3 Sep 2024 20:48:53 -0400 "Liam R. Howlett" wrote: > * SeongJae Park [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 > > Closes: https://lore.kernel.org/1453b2b2-6119-4082-ad9e-f3c5239bf87e@roeck-us.net > > Fixes: d0cf3dd47f0d ("damon: convert __damon_va_three_regions to use the VMA iterator") > > Signed-off-by: SeongJae Park > > --- > > 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 > >