From: Jon Derrick Subject: [PATCH] ext4: Check superblock mapped prior to committing Date: Fri, 29 Jun 2018 13:36:35 -0600 Message-ID: <1530300995-25583-1-git-send-email-jonathan.derrick@intel.com> Cc: "Theodore Ts'o" , Andreas Dilger , , Jon Derrick To: Return-path: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org 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 --- fs/ext4/super.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 0c4c220..ee33233 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -4736,6 +4736,14 @@ 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 -- 2.7.4