From 917692c9cdf5ea62e783d08dfef40bfb982a9dca Mon Sep 17 00:00:00 2001 From: Jon Derrick Date: Mon, 2 Jul 2018 18:45:18 -0400 Subject: [PATCH] ext4: check superblock mapped prior to committing commit a17712c8e4be4fa5404d20e9cd3b2b21eae7bc56 upstream. This patch attempts to close a hole leading to a BUG seen with hot removals during writes [1]. A block device (NVME namespace in this test case) is formatted to EXT4 without partitions. It's mounted and write I/O is run to a file, then the device is hot removed from the slot. The superblock attempts to be written to the drive which is no longer present. The typical chain of events leading to the BUG: ext4_commit_super() __sync_dirty_buffer() submit_bh() submit_bh_wbc() BUG_ON(!buffer_mapped(bh)); This fix checks for the superblock's buffer head being mapped prior to syncing. [1] https://www.spinics.net/lists/linux-ext4/msg56527.html Signed-off-by: Jon Derrick Signed-off-by: Theodore Ts'o Cc: stable@kernel.org Signed-off-by: Greg Kroah-Hartman --- fs/ext4/super.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/fs/ext4/super.c b/fs/ext4/super.c index fff215a1f1a9..41ef83471ea5 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -4629,6 +4629,14 @@ static int ext4_commit_super(struct super_block *sb, int sync) if (!sbh || block_device_ejected(sb)) return error; + + /* + * The superblock bh should be mapped, but it might not be if the + * device was hot-removed. Not much we can do but fail the I/O. + */ + if (!buffer_mapped(sbh)) + return error; + /* * If the file system is mounted read-only, don't update the * superblock write time. This avoids updating the superblock -- 2.20.1