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Sat, 19 Oct 2019 03:20:16 +0000 (UTC) Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 393B822468; Sat, 19 Oct 2019 03:20:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571455215; bh=N/iUHVGm7NC7r721VMBmrmymMT3Cc/PZyZIjY0Jy73U=; h=Date:From:To:Subject:From; b=sp6ztH3mYRlbskEwsjYx7hqyLf08QBspii6u5RcawlHxCmTA5UW6Xz+ngVdxOSxdE 8dqBU37lx86rbNWvCNLDlNeUWhevsLs7H90LsBEcwKvorEl0NNhrXXmSzquEOYd4QC FCTf3AaJKqLKhQ+VIkq1xH4xQ2tsEdYxF0gDJZqw= Date: Fri, 18 Oct 2019 20:20:14 -0700 From: akpm@linux-foundation.org To: akpm@linux-foundation.org, axboe@kernel.dk, chenwandun@huawei.com, linux-mm@kvack.org, minchan@kernel.org, mm-commits@vger.kernel.org, sergey.senozhatsky.work@gmail.com, stable@vger.kernel.org, torvalds@linux-foundation.org Subject: [patch 17/26] zram: fix race between backing_dev_show and backing_dev_store Message-ID: <20191019032014.mkysg81b4%akpm@linux-foundation.org> User-Agent: s-nail v14.8.16 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: From: Chenwandun Subject: zram: fix race between backing_dev_show and backing_dev_store CPU0: CPU1: backing_dev_show backing_dev_store ...... ...... file = zram->backing_dev; down_read(&zram->init_lock); down_read(&zram->init_init_lock) file_path(file, ...); zram->backing_dev = backing_dev; up_read(&zram->init_lock); up_read(&zram->init_lock); gets the value of zram->backing_dev too early in backing_dev_show, which resultin the value being NULL at the beginning, and not NULL later. backtrace: [] d_path+0xcc/0x174 [] file_path+0x10/0x18 [] backing_dev_show+0x40/0xb4 [] dev_attr_show+0x20/0x54 [] sysfs_kf_seq_show+0x9c/0x10c [] kernfs_seq_show+0x28/0x30 [] seq_read+0x184/0x488 [] kernfs_fop_read+0x5c/0x1a4 [] __vfs_read+0x44/0x128 [] vfs_read+0xa0/0x138 [] SyS_read+0x54/0xb4 Link: http://lkml.kernel.org/r/1571046839-16814-1-git-send-email-chenwandun@huawei.com Signed-off-by: Chenwandun Acked-by: Minchan Kim Cc: Sergey Senozhatsky Cc: Jens Axboe Cc: [4.14+] Signed-off-by: Andrew Morton --- drivers/block/zram/zram_drv.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/drivers/block/zram/zram_drv.c~zram-fix-race-between-backing_dev_show-and-backing_dev_store +++ a/drivers/block/zram/zram_drv.c @@ -413,13 +413,14 @@ static void reset_bdev(struct zram *zram static ssize_t backing_dev_show(struct device *dev, struct device_attribute *attr, char *buf) { + struct file *file; struct zram *zram = dev_to_zram(dev); - struct file *file = zram->backing_dev; char *p; ssize_t ret; down_read(&zram->init_lock); - if (!zram->backing_dev) { + file = zram->backing_dev; + if (!file) { memcpy(buf, "none\n", 5); up_read(&zram->init_lock); return 5; _