4.4-stable review patch. If anyone has any objections, please let me know.
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From: Jon Derrick jonathan.derrick@intel.com
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 jonathan.derrick@intel.com Signed-off-by: Theodore Ts'o tytso@mit.edu Cc: stable@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/ext4/super.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -4442,6 +4442,14 @@ static int ext4_commit_super(struct supe
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 (buffer_write_io_error(sbh)) { /* * Oh, dear. A previous attempt to write the