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Wed, 09 Aug 2023 11:08:36 -0700 (PDT) MIME-Version: 1.0 References: <20230630211957.1341547-1-surenb@google.com> <0ab6524a-6917-efe2-de69-f07fb5cdd9d2@redhat.com> In-Reply-To: <0ab6524a-6917-efe2-de69-f07fb5cdd9d2@redhat.com> From: Suren Baghdasaryan Date: Wed, 9 Aug 2023 11:08:23 -0700 Message-ID: Subject: Re: [PATCH v7 0/6] Per-VMA lock support for swap and userfaults To: David Hildenbrand Cc: akpm@linux-foundation.org, willy@infradead.org, hannes@cmpxchg.org, mhocko@suse.com, josef@toxicpanda.com, jack@suse.cz, ldufour@linux.ibm.com, laurent.dufour@fr.ibm.com, michel@lespinasse.org, liam.howlett@oracle.com, jglisse@google.com, vbabka@suse.cz, minchan@google.com, dave@stgolabs.net, punit.agrawal@bytedance.com, lstoakes@gmail.com, hdanton@sina.com, apopple@nvidia.com, peterx@redhat.com, ying.huang@intel.com, yuzhao@google.com, dhowells@redhat.com, hughd@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, pasha.tatashin@soleen.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 77183120028 X-Stat-Signature: p4rb4auuk7to93rwz6w4nfjjqg5ewn46 X-Rspam-User: X-HE-Tag: 1691604517-353374 X-HE-Meta: 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 JB9shvPq rdYuoAKYK2oULc+8ZHk1+853VmLHPRgs6vnAew78n1Dda6QmW5N+louv9w9O7QXk1ZAye13dyEwnI9BiwHRJDzK/DngtXw/IxYbwj3W2Fwmtn7jwCzyrVMpx+0a6EHWKpA9J7tD9V3dEd7CctcsKTwdU0zsg6enZEhBquU0u41ZL1IKMAIzdejAgH9DxVj0inH9ALs/bHJLSuDbU52NLcbKcGXUUd0mcF2awRgHW0Oz4mEmmENkzUcFUsVA== 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: On Wed, Aug 9, 2023 at 11:04=E2=80=AFAM David Hildenbrand wrote: > > >>>> Which ends up being > >>>> > >>>> VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm); > >>>> > >>>> I did not check if this is also the case on mainline, and if this se= ries is responsible. > >>> > >>> Thanks for reporting! I'm checking it now. > >> > >> Hmm. From the code it's not obvious how lock_mm_and_find_vma() ends up > >> calling find_vma() without mmap_lock after successfully completing > >> get_mmap_lock_carefully(). lock_mm_and_find_vma+0x3f/0x270 points to > >> the first invocation of find_vma(), so this is not even the lock > >> upgrade path... I'll try to reproduce this issue and dig up more but > >> from the information I have so far this issue does not seem to be > >> related to this series. > > I just checked on mainline and it does not fail there. > > > > > This is really weird. I added mmap_assert_locked(mm) calls into > > get_mmap_lock_carefully() right after we acquire mmap_lock read lock > > and one of them triggers right after successful > > mmap_read_lock_killable(). Here is my modified version of > > get_mmap_lock_carefully(): > > > > static inline bool get_mmap_lock_carefully(struct mm_struct *mm, > > struct pt_regs *regs) { > > /* Even if this succeeds, make it clear we might have slept */ > > if (likely(mmap_read_trylock(mm))) { > > might_sleep(); > > mmap_assert_locked(mm); > > return true; > > } > > if (regs && !user_mode(regs)) { > > unsigned long ip =3D instruction_pointer(regs); > > if (!search_exception_tables(ip)) > > return false; > > } > > if (!mmap_read_lock_killable(mm)) { > > mmap_assert_locked(mm); <---- generates a= BUG > > return true; > > } > > return false; > > } > > Ehm, that's indeed weird. > > > > > AFAIKT conditions for mmap_read_trylock() and > > mmap_read_lock_killable() are checked correctly. Am I missing > > something? > > Weirdly enough, it only triggers during that specific uffd test, right? Yes, uffd-unit-tests. I even ran it separately to ensure it's not some fallback from a previous test and I'm able to reproduce this consistently. > > -- > Cheers, > > David / dhildenb >