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AJvYcCWy3eFrN0/08wSGUU+IGjNnYt1LziHliPq4KN5IMBHs5aVrPARmLc78cqghVXrsGcVJ6w8f/EvzfpitZljbc5dJCHXlyjAjPWeCRvB46A== X-Gm-Message-State: AOJu0Yz58Ftl/16CR0zda3qVAzUMC8MuTbC6X/B+yO+JOmz4K2rW4NB8 VcbwSrwybIMTHR8DRItHPbjy9I5iMkTHAVcEgu8i0/ItwrlNZJY2sKepJiy7uUPX7otjG3fPveE mFnVMWKgCkWkM+8Tix0USZ/MaWW4TEUuHcHv5 X-Google-Smtp-Source: AGHT+IFqS8tJn14NncAWY62WTNABteq4kVyKmIkcCAlDBmY1N2BQti8G3zCHf537pCEhp7uq+qbCNuxgh3NLwozuq4M= X-Received: by 2002:a5b:bcc:0:b0:dc7:32ae:f0a with SMTP id c12-20020a5b0bcc000000b00dc732ae0f0amr80411ybr.65.1708539977180; Wed, 21 Feb 2024 10:26:17 -0800 (PST) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <320cd134-b767-4f29-869b-d219793ba8a1@suse.cz> <20240215180742.34470209@gandalf.local.home> <20240215181648.67170ed5@gandalf.local.home> <20240215182729.659f3f1c@gandalf.local.home> In-Reply-To: From: Suren Baghdasaryan Date: Wed, 21 Feb 2024 10:26:04 -0800 Message-ID: Subject: Re: [PATCH v3 31/35] lib: add memory allocations report in show_mem() To: Tetsuo Handa Cc: Vlastimil Babka , Kent Overstreet , Steven Rostedt , Michal Hocko , akpm@linux-foundation.org, hannes@cmpxchg.org, roman.gushchin@linux.dev, mgorman@suse.de, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, corbet@lwn.net, void@manifault.com, peterz@infradead.org, juri.lelli@redhat.com, catalin.marinas@arm.com, will@kernel.org, arnd@arndb.de, tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, x86@kernel.org, peterx@redhat.com, david@redhat.com, axboe@kernel.dk, mcgrof@kernel.org, masahiroy@kernel.org, nathan@kernel.org, dennis@kernel.org, tj@kernel.org, muchun.song@linux.dev, rppt@kernel.org, paulmck@kernel.org, pasha.tatashin@soleen.com, yosryahmed@google.com, yuzhao@google.com, dhowells@redhat.com, hughd@google.com, andreyknvl@gmail.com, keescook@chromium.org, ndesaulniers@google.com, vvvvvv@google.com, gregkh@linuxfoundation.org, ebiggers@google.com, ytcoode@gmail.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, bsegall@google.com, bristot@redhat.com, vschneid@redhat.com, cl@linux.com, penberg@kernel.org, iamjoonsoo.kim@lge.com, 42.hyeyoo@gmail.com, glider@google.com, elver@google.com, dvyukov@google.com, shakeelb@google.com, songmuchun@bytedance.com, jbaron@akamai.com, rientjes@google.com, minchan@google.com, kaleshsingh@google.com, kernel-team@android.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, iommu@lists.linux.dev, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-modules@vger.kernel.org, kasan-dev@googlegroups.com, cgroups@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, Feb 21, 2024 at 5:22=E2=80=AFAM Tetsuo Handa wrote: > > On 2024/02/21 3:27, Vlastimil Babka wrote: > > I'm sure more such scenarios exist, Cc: Tetsuo who I recall was an expe= rt on > > this topic. > > "[PATCH v3 10/35] lib: code tagging framework" says that codetag_lock_mod= ule_list() > calls down_read() (i.e. sleeping operation), and > "[PATCH v3 31/35] lib: add memory allocations report in show_mem()" says = that > __show_mem() calls alloc_tags_show_mem_report() after kmalloc(GFP_ATOMIC)= (i.e. > non-sleeping operation) but alloc_tags_show_mem_report() calls down_read(= ) via > codetag_lock_module_list() !? > > If __show_mem() might be called from atomic context (e.g. kmalloc(GFP_ATO= MIC)), > this will be a sleep in atomic bug. > If __show_mem() might be called while semaphore is held for write, > this will be a read-lock after write-lock deadlock bug. > > Not the matter of whether to allocate buffer statically or dynamically. > Please don't hold a lock when trying to report memory usage. Thanks for catching this, Tetsuo! Yes, we take the read-lock here to ensure that the list of modules is stable. I'm thinking I can replace the down_read() with down_read_trylock() and if we fail (there is a race with module load/unload) we will skip generating this report. The probability of racing with module load/unload while in OOM state I think is quite low, so skipping this report should not cause much information loss. > >