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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Minchan Kim <minchan@kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Joey Pabalinas <joeypabalinas@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: [PATCH 4.20 04/65] zram: fix double free backing device
Date:   Fri, 11 Jan 2019 15:14:50 +0100
Message-Id: <20190111131056.679232043@linuxfoundation.org>
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4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Minchan Kim <minchan@kernel.org>

commit 5547932dc67a48713eece4fa4703bfdf0cfcb818 upstream.

If blkdev_get fails, we shouldn't do blkdev_put.  Otherwise, kernel emits
below log.  This patch fixes it.

  WARNING: CPU: 0 PID: 1893 at fs/block_dev.c:1828 blkdev_put+0x105/0x120
  Modules linked in:
  CPU: 0 PID: 1893 Comm: swapoff Not tainted 4.19.0+ #453
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
  RIP: 0010:blkdev_put+0x105/0x120
  Call Trace:
    __x64_sys_swapoff+0x46d/0x490
    do_syscall_64+0x5a/0x190
    entry_SYSCALL_64_after_hwframe+0x49/0xbe
  irq event stamp: 4466
  hardirqs last  enabled at (4465):  __free_pages_ok+0x1e3/0x490
  hardirqs last disabled at (4466):  trace_hardirqs_off_thunk+0x1a/0x1c
  softirqs last  enabled at (3420):  __do_softirq+0x333/0x446
  softirqs last disabled at (3407):  irq_exit+0xd1/0xe0

Link: http://lkml.kernel.org/r/20181127055429.251614-3-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reviewed-by: Joey Pabalinas <joeypabalinas@gmail.com>
Cc: <stable@vger.kernel.org>	[4.14+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/block/zram/zram_drv.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -382,8 +382,10 @@ static ssize_t backing_dev_store(struct
 
 	bdev = bdgrab(I_BDEV(inode));
 	err = blkdev_get(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL, zram);
-	if (err < 0)
+	if (err < 0) {
+		bdev = NULL;
 		goto out;
+	}
 
 	nr_pages = i_size_read(inode) >> PAGE_SHIFT;
 	bitmap_sz = BITS_TO_LONGS(nr_pages) * sizeof(long);