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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=ov2HI3CdUQ+o/zqidsM3mX5Kp69NRx9NtPM0yxA19Es=; b=RQA1MwHYfbOkbgCViNvnfcfGFbJjSneRg4eieiNyvNyr+kJTvLPnnUYR0Ij7h5kMEi xbQg/gSL88DOtM0d96NEZV+777/ZYdyox+wX6ueNJmth0tUezCB3upDxYY2Wp7SutZpK U6ILA4IS/UDAjREG7JO7WbLCaGBm/YoiwGeUaligWI1FwFhtuq+MXAjNKkTBAgL54YId 6Y6rTafsfuCJsedsofd1BGC/8Z1FtG8Kjmg3zk4nEJPp/gRvEJKpFmN7osn4Pn+otveR zia+4gylvSvvObB2GdUuSb+4JWO+P55BPpgSnCqjS8V5idS/UHxj4Bp6ybfGbQ1fyxpP mQuQ== X-Gm-Message-State: AFqh2kppCAehGZpnTFWgcMRzybgP+QtJ9RKWMlI2aTUQTvsNClrJqNlP i5tEhl2Fa5K4DixZes1XHxwp2dJuwiRXuBqinjU1kQ== X-Google-Smtp-Source: AMrXdXvNbPUYj/FTXP9jMwGpFUtrl5UX+b/2dnT1jMx2j8lGwbfTbtmjUt5vhRCKMdkNLOmIJWYnhuJB9a8X5pfKXE8= X-Received: by 2002:a81:6d8d:0:b0:490:89c3:21b0 with SMTP id i135-20020a816d8d000000b0049089c321b0mr610621ywc.132.1673990920942; Tue, 17 Jan 2023 13:28:40 -0800 (PST) MIME-Version: 1.0 References: <20230109205336.3665937-1-surenb@google.com> <20230109205336.3665937-13-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Tue, 17 Jan 2023 13:28:27 -0800 Message-ID: Subject: Re: [PATCH 12/41] mm: add per-VMA lock and helper functions to control it To: Jann Horn Cc: peterz@infradead.org, Ingo Molnar , Will Deacon , 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, 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_132842_494188_EE8A9EB6 X-CRM114-Status: GOOD ( 22.84 ) 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 10:03 AM Jann Horn wrote: > > +locking maintainers Thanks! I'll CC the locking maintainers in the next posting. > > On Mon, Jan 9, 2023 at 9:54 PM Suren Baghdasaryan wrote: > > Introduce a per-VMA rw_semaphore to be used during page fault handling > > instead of mmap_lock. Because there are cases when multiple VMAs need > > to be exclusively locked during VMA tree modifications, instead of the > > usual lock/unlock patter we mark a VMA as locked by taking per-VMA lock > > exclusively and setting vma->lock_seq to the current mm->lock_seq. When > > mmap_write_lock holder is done with all modifications and drops mmap_lock, > > it will increment mm->lock_seq, effectively unlocking all VMAs marked as > > locked. > [...] > > +static inline void vma_read_unlock(struct vm_area_struct *vma) > > +{ > > + up_read(&vma->lock); > > +} > > One thing that might be gnarly here is that I think you might not be > allowed to use up_read() to fully release ownership of an object - > from what I remember, I think that up_read() (unlike something like > spin_unlock()) can access the lock object after it's already been > acquired by someone else. So if you want to protect against concurrent > deletion, this might have to be something like: > > rcu_read_lock(); /* keeps vma alive */ > up_read(&vma->lock); > rcu_read_unlock(); But for deleting VMA one would need to write-lock the vma->lock first, which I assume can't happen until this up_read() is complete. Is that assumption wrong? > > But I'm not entirely sure about that, the locking folks might know better. > > Also, it might not matter given that the rw_semaphore part is removed > in the current patch 41/41 anyway... This does matter because Michal suggested dropping that last 41/41 patch for now. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel