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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=4j3tl0DYASqrjkqUxwz46bG4ROPSgLPddwJUIyGPfX8=; b=7TM/UMt/lDGJPHv9FRGWbvNl2W3Qx61fcM7hkLWLqkqGPW5hjLl5+q0zs3dFA0LQJp Zwuc5GXWvvwYMJPWVBprHFOKVhi6S6fqctWi3FujkWrFQSIkbkxtRMdIW6chQpltotdz Rkx5Kk87SHWOpphg54xh5qStPknaoIaUVo6aYmDwKQ01OGP9LP8jEg4BUf4XnqvvfHkZ AhV8JwlOSOQPk4NbHvwGrG9ymyLewVBW1EsRX99gc/RuTBaYJeNf7xfkSncbLBXBEDfY 7nnEQDArFJ8edAOTwe6DSElZSzr7Uy8sU9TBQW6blX2UhpSdSvm6/q5V3WHZsA9JFjax VIHw== X-Gm-Message-State: AFqh2ko79vhRcmJs43vCT+djzX4cfr+3V2Cr7Wp8XWJ5ZJ4Q/tPtrA2l akBXNdvv+ZZI7CKRgyDrqFpX6GRG6NTfkpjsmFkoZg== X-Google-Smtp-Source: AMrXdXs7BogT7SdoZ360ei40N37ZNOM5XxWUzxAMlDXlaXiTGADLynxjLDtiuGW4hqoQrK26rMYv0lMAFrNqu+/4diM= X-Received: by 2002:a25:ceca:0:b0:7e4:115c:9cf6 with SMTP id x193-20020a25ceca000000b007e4115c9cf6mr537549ybe.316.1673980003301; Tue, 17 Jan 2023 10:26:43 -0800 (PST) MIME-Version: 1.0 References: <20230109205336.3665937-1-surenb@google.com> <20230109205336.3665937-42-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Tue, 17 Jan 2023 10:26:32 -0800 Message-ID: Subject: Re: [PATCH 41/41] mm: replace rw_semaphore with atomic_t in vma_lock To: Jann Horn Cc: akpm@linux-foundation.org, michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org, ldufour@linux.ibm.com, laurent.dufour@fr.ibm.com, paulmck@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, punit.agrawal@bytedance.com, lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, shakeelb@google.com, tatashin@google.com, edumazet@google.com, gthelen@google.com, gurua@google.com, arjunroy@google.com, soheil@google.com, hughlynch@google.com, leewalsh@google.com, posk@google.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230117_102646_873547_8FE3A0E8 X-CRM114-Status: GOOD ( 15.57 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Jan 17, 2023 at 10:12 AM Jann Horn wrote: > > On Mon, Jan 9, 2023 at 9:55 PM Suren Baghdasaryan wrote: > > rw_semaphore is a sizable structure of 40 bytes and consumes > > considerable space for each vm_area_struct. However vma_lock has > > two important specifics which can be used to replace rw_semaphore > > with a simpler structure: > [...] > > static inline void vma_read_unlock(struct vm_area_struct *vma) > > { > > - up_read(&vma->vm_lock->lock); > > + if (atomic_dec_and_test(&vma->vm_lock->count)) > > + wake_up(&vma->vm_mm->vma_writer_wait); > > } > > I haven't properly reviewed this, but this bit looks like a > use-after-free because you're accessing the vma after dropping your > reference on it. You'd have to first look up the vma->vm_mm, then do > the atomic_dec_and_test(), and afterwards do the wake_up() without > touching the vma. Or alternatively wrap the whole thing in an RCU > read-side critical section if the VMA is freed with RCU delay. vm_lock->count does not control the lifetime of the VMA, it's a counter of how many readers took the lock or it's negative if the lock is write-locked. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel