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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pjBWW-00DmMZ-Hj; Mon, 03 Apr 2023 04:10:28 +0000 Date: Mon, 3 Apr 2023 05:10:28 +0100 From: Matthew Wilcox To: Rongwei Wang Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-stable@vger.kernel.org Subject: Re: [PATCH] mm/swap: fix swap_info_struct race between swapoff and get_swap_pages() Message-ID: References: <20230401221920.57986-1-rongwei.wang@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230401221920.57986-1-rongwei.wang@linux.alibaba.com> X-Rspamd-Queue-Id: B494720004 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: xjg8fcigjbfg3a4heap8muyaywi8iaoe X-HE-Tag: 1680495035-591141 X-HE-Meta: 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 SRtKX1Xv fTXY5thP5I2g+TdqQ0BmM/QBkHPNhRbLxgQAUhJbV/anCmb0IU5jjBoCncrrvMg/G2k3lEAH2C1pkpMXmvIF8N15GhWwhQq+DDk+iCbHYhI2tOyJI/a2lGYO/EUHI/9J2OqojfL1Ex5qTdjCXS4nCm7TijYsr+1Z7zrzmdptNV1RQGGqPb4lfybt9AlO9FkhdHKD6Y5/2NtAIHB4= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, Apr 02, 2023 at 06:19:20AM +0800, Rongwei Wang wrote: > Without this modification, a core will wait (mostly) > 'swap_info_struct->lock' when completing > 'del_from_avail_list(p)'. Immediately, other cores > soon calling 'add_to_avail_list()' to add the same > object again when acquiring the lock that released > by former. It's not the desired result but exists > indeed. This case can be described as below: This feels like a very verbose way of saying "The si->lock must be held when deleting the si from the available list. Otherwise, another thread can re-add the si to the available list, which can lead to memory corruption. The only place we have found where this happens is in the swapoff path." > +++ b/mm/swapfile.c > @@ -2610,8 +2610,12 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) > spin_unlock(&swap_lock); > goto out_dput; > } > - del_from_avail_list(p); > + /* > + * Here lock is used to protect deleting and SWP_WRITEOK clearing > + * can be seen concurrently. > + */ This comment isn't necessary. But I would add a lockdep assert inside __del_from_avail_list() that p->lock is held. > spin_lock(&p->lock); > + del_from_avail_list(p); > if (p->prio < 0) { > struct swap_info_struct *si = p; > int nid; > -- > 2.27.0 > >