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Thu, 28 Nov 2024 01:14:35 -0800 (PST) MIME-Version: 1.0 References: <20241122154051.3914732-1-elver@google.com> <20241127172523.b12b82d150aad5069e024645@linux-foundation.org> In-Reply-To: <20241127172523.b12b82d150aad5069e024645@linux-foundation.org> From: Marco Elver Date: Thu, 28 Nov 2024 10:13:59 +0100 Message-ID: Subject: Re: [PATCH] stackdepot: fix stack_depot_save_flags() in NMI context To: Andrew Morton Cc: Andrey Konovalov , Alexander Potapenko , Dmitry Vyukov , Vlastimil Babka , Oscar Salvador , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kasan-dev@googlegroups.com, Sebastian Andrzej Siewior Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 461262000D X-Stat-Signature: rcb544p83uki7cjf1ebhbhq5we3ecsye X-HE-Tag: 1732785274-996048 X-HE-Meta: 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 K/quFdzY wmxuvB3tFGPS4fTRM6bLrnzZxe5J9rP4QdTjMDmNu8MpFzl0mOIIGidZqoNZDW3y66wDg4tcBnbGmx2Tu2e1U8IGLPSUVBEsfzcj2JcPgqqJzRQbD9vj+S2fpc7Bp+EEwasrzFYtbcv9Tkc/opReCNJWR6belwHdJ54P9Sbdmr9jJITe2iYKJG5FFWinnT2EwTi3yIn6EwxPb24RyP7FnJ981QxP0P0aPrnxqEVr6WoTIbBsp7WfdsjmRHsZZVEaa2Dh0KkAHFMlhcVbIhG2csdz2hGBoimM2XGdiJ5qmPeJ2nb2ccv5m/l1DR6HVbMoOAJavVuezJ/oy89Y8LgcARhGwolDVB/hxTubFcnqF08TEs24tCqLRhXgB8w== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000045, 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 Thu, 28 Nov 2024 at 02:25, Andrew Morton wrote: > > On Fri, 22 Nov 2024 16:39:47 +0100 Marco Elver wrote: > > > Per documentation, stack_depot_save_flags() was meant to be usable from > > NMI context if STACK_DEPOT_FLAG_CAN_ALLOC is unset. However, it still > > would try to take the pool_lock in an attempt to save a stack trace in > > the current pool (if space is available). > > > > This could result in deadlock if an NMI is handled while pool_lock is > > already held. To avoid deadlock, only try to take the lock in NMI > > context and give up if unsuccessful. > > Is it possible to trigger this deadlock in current kernels, or is this > a might-happen-in-the-future thing? I can't find evidence this happens right now (at least with the quick test I just ran), so it's more of a might happen if use of this API broadens. Thanks, -- Marco