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Fri, 20 Jan 2023 22:44:02 -0500 (EST) Date: Fri, 20 Jan 2023 19:44:01 -0800 From: Boqun Feng To: Byungchul Park Cc: linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, damien.lemoal@opensource.wdc.com, linux-ide@vger.kernel.org, adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, mingo@redhat.com, peterz@infradead.org, will@kernel.org, tglx@linutronix.de, rostedt@goodmis.org, joel@joelfernandes.org, sashal@kernel.org, daniel.vetter@ffwll.ch, duyuyang@gmail.com, johannes.berg@intel.com, tj@kernel.org, tytso@mit.edu, willy@infradead.org, david@fromorbit.com, amir73il@gmail.com, gregkh@linuxfoundation.org, kernel-team@lge.com, linux-mm@kvack.org, akpm@linux-foundation.org, mhocko@kernel.org, minchan@kernel.org, hannes@cmpxchg.org, vdavydov.dev@gmail.com, sj@kernel.org, jglisse@redhat.com, dennis@kernel.org, cl@linux.com, penberg@kernel.org, rientjes@google.com, vbabka@suse.cz, ngupta@vflare.org, linux-block@vger.kernel.org, paolo.valente@linaro.org, josef@toxicpanda.com, linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, jack@suse.cz, jlayton@kernel.org, dan.j.williams@intel.com, hch@infradead.org, djwong@kernel.org, dri-devel@lists.freedesktop.org, rodrigosiqueiramelo@gmail.com, melissa.srw@gmail.com, hamohammed.sa@gmail.com, 42.hyeyoo@gmail.com, chris.p.wilson@intel.com, gwan-gyeong.mun@intel.com, max.byungchul.park@gmail.com, longman@redhat.com Subject: Re: [PATCH RFC v7 00/23] DEPT(Dependency Tracker) Message-ID: References: <1674271694-18950-1-git-send-email-byungchul.park@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1674271694-18950-1-git-send-email-byungchul.park@lge.com> X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: AA9994000F X-Rspam-User: X-Stat-Signature: adopythbpjsyt1eu4gig8p7dy7hdetci X-HE-Tag: 1674272655-69637 X-HE-Meta: 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 h1Ag4xTc 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 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 Sat, Jan 21, 2023 at 12:28:14PM +0900, Byungchul Park wrote: > On Thu, Jan 19, 2023 at 07:07:59PM -0800, Boqun Feng wrote: > > On Thu, Jan 19, 2023 at 06:23:49PM -0800, Boqun Feng wrote: > > > On Fri, Jan 20, 2023 at 10:51:45AM +0900, Byungchul Park wrote: > > [...] > > > > > T0 T1 T2 > > > > -- -- -- > > > > unfair_read_lock(A); > > > > write_lock(B); > > > > write_lock(A); > > > > write_lock(B); > > > > fair_read_lock(A); > > > > write_unlock(B); > > > > read_unlock(A); > > > > read_unlock(A); > > > > write_unlock(B); > > > > write_unlock(A); > > > > > > > > T0: read_unlock(A) cannot happen if write_lock(B) is stuck by a B owner > > > > not doing either write_unlock(B) or read_unlock(B). In other words: > > > > > > > > 1. read_unlock(A) happening depends on write_unlock(B) happening. > > > > 2. read_unlock(A) happening depends on read_unlock(B) happening. > > > > > > > > T1: write_unlock(B) cannot happen if fair_read_lock(A) is stuck by a A > > > > owner not doing either write_unlock(A) or read_unlock(A). In other > > > > words: > > > > > > > > 3. write_unlock(B) happening depends on write_unlock(A) happening. > > > > 4. write_unlock(B) happening depends on read_unlock(A) happening. > > > > > > > > 1, 2, 3 and 4 give the following dependencies: > > > > > > > > 1. read_unlock(A) -> write_unlock(B) > > > > 2. read_unlock(A) -> read_unlock(B) > > > > 3. write_unlock(B) -> write_unlock(A) > > > > 4. write_unlock(B) -> read_unlock(A) > > > > > > > > With 1 and 4, there's a circular dependency so DEPT definitely report > > > > this as a problem. > > > > > > > > REMIND: DEPT focuses on waits and events. > > > > > > Do you have the test cases showing DEPT can detect this? > > > > > > > Just tried the following on your latest GitHub branch, I commented all > > but one deadlock case. Lockdep CAN detect it but DEPT CANNOT detect it. > > Feel free to double check. > > I tried the 'queued read lock' test cases with DEPT on. I can see DEPT > detect and report it. But yeah.. it's too verbose now. It's because DEPT > is not aware of the test environment so it's just working hard to report > every case. > > To make DEPT work with the selftest better, some works are needed. I > will work on it later or you please work on it. > > The corresponding report is the following. > [...] > [ 4.593037] context A's detail > [ 4.593351] --------------------------------------------------- > [ 4.593944] context A > [ 4.594182] [S] lock(&rwlock_A:0) > [ 4.594577] [W] lock(&rwlock_B:0) > [ 4.594952] [E] unlock(&rwlock_A:0) > [ 4.595341] > [ 4.595501] [S] lock(&rwlock_A:0): > [ 4.595848] [] queued_read_lock_hardirq_ER_rE+0xf4/0x170 > [ 4.596547] stacktrace: > [ 4.596797] _raw_read_lock+0xcf/0x110 > [ 4.597215] queued_read_lock_hardirq_ER_rE+0xf4/0x170 > [ 4.597766] dotest+0x30/0x7bc > [ 4.598118] locking_selftest+0x2c6f/0x2ead > [ 4.598602] start_kernel+0x5aa/0x6d5 > [ 4.599017] secondary_startup_64_no_verify+0xe0/0xeb > [ 4.599562] [...] > [ 4.608427] [] queued_read_lock_hardirq_RE_Er+0xf4/0x170 > [ 4.609113] stacktrace: > [ 4.609366] _raw_write_lock+0xc3/0xd0 > [ 4.609788] queued_read_lock_hardirq_RE_Er+0xf4/0x170 > [ 4.610371] dotest+0x30/0x7bc > [ 4.610730] locking_selftest+0x2c41/0x2ead > [ 4.611195] start_kernel+0x5aa/0x6d5 > [ 4.611615] secondary_startup_64_no_verify+0xe0/0xeb > [ 4.612164] > [ 4.612325] [W] lock(&rwlock_A:0): > [ 4.612671] [] queued_read_lock_hardirq_RE_Er+0x100/0x170 > [ 4.613369] stacktrace: > [ 4.613622] _raw_read_lock+0xac/0x110 > [ 4.614047] queued_read_lock_hardirq_RE_Er+0x100/0x170 > [ 4.614652] dotest+0x30/0x7bc > [ 4.615007] locking_selftest+0x2c41/0x2ead > [ 4.615468] start_kernel+0x5aa/0x6d5 > [ 4.615879] secondary_startup_64_no_verify+0xe0/0xeb > [ 4.616607] [...] > As I told you, DEPT treats a queued lock as a normal type lock, no > matter whether it's a read lock. That's why it prints just > 'lock(&rwlock_A:0)' instead of 'read_lock(&rwlock_A:0)'. If needed, I'm > gonna change the format. > > I checked the selftest code and found, LOCK(B) is transformed like: > > LOCK(B) -> WL(B) -> write_lock(&rwlock_B) > > That's why '&rwlock_B' is printed instead of just 'B', JFYI. > Nah, you output shows that you've run at least both function queued_read_lock_hardirq_RE_Er() queued_read_lock_hardirq_ER_rE() but if you apply my diff https://lore.kernel.org/lkml/Y8oFj9A19cw3enHB@boqun-archlinux/ you should only run queued_read_lock_hardirq_RE_Er() one test. One of the reason that DEPT "detect" this is that DEPT doesn't reset between tests, so old dependencies from previous run get carried over. > Plus, for your information, you should turn on CONFIG_DEPT to use it. > Yes I turn that config on. Regards, Boqun > Byungchul