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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=dcrz3u05liU0MW9kY4AJIlBTNw63wTKDLbyoxh2Gq7o=; b=4k3N0uKBT9P/LrOmb3myyqmpgany9cOxwXqTJ9gplfe4Hv8iuo1LOfmb/0erPtsqrt yCyV3/Kw7friUOauszGz5tK7E410aV/yRFeioF+pN4JYCMIvBzuyGw/FjoCo4CbCS0uH JYgYPupMlQGDJu96lZnqT9C1RY3v2EVK7i2bI/Ij+3o1pEoy8wAkoM6GVoYpCstrCPBz fCSUCp5ayh8TXdEBzWRVikGOZ8eMEb9+d0EwjjQasL3pb6QiL9M79dtIW1To4+qEsPa/ T2qQf2FTChL8dZeYpmJ8t0blaOJibSW5s82UvIIBqFp2tLzajaH9JItivu028DhqKfFM Kw9A== X-Gm-Message-State: AFqh2ko8Ai4dL9ngM5HjX8HIvSddlktAM77LdAO3QM0tQscv6OE4dSSM BYdgNRgLnLwSn2FJo7v6kX1LoxZ71UGGy7Kes+GRhw== X-Google-Smtp-Source: AMrXdXsgW7Mw7qSRUXKXfN+rdxMVcw5NgXHaFtzV+np+Si6HoBmXxOeDmNDFe8VfWaSsmByezu+xjIBOp9/ez1+o9/0= X-Received: by 2002:a02:c884:0:b0:39e:9d33:a47 with SMTP id m4-20020a02c884000000b0039e9d330a47mr264435jao.58.1673979122352; Tue, 17 Jan 2023 10:12:02 -0800 (PST) MIME-Version: 1.0 References: <20230109205336.3665937-1-surenb@google.com> <20230109205336.3665937-42-surenb@google.com> In-Reply-To: <20230109205336.3665937-42-surenb@google.com> From: Jann Horn Date: Tue, 17 Jan 2023 19:11:26 +0100 Message-ID: Subject: Re: [PATCH 41/41] mm: replace rw_semaphore with atomic_t in vma_lock To: Suren Baghdasaryan 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 Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 38BE540012 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: ttqnsofe5skw7pw7nykra81npagzmpby X-HE-Tag: 1673979123-672191 X-HE-Meta: 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 0Tr2sv9U xrK1FOr9Td8dYAzCp/v2n8WIQGHB7/G2kHoYNOcGCkNN1coBJKLu2NqMYUQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.001902, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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.