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Btrfs: remove superblock writing after fatal error
With commit acce952b, btrfs was changed to flag the filesystem with BTRFS_SUPER_FLAG_ERROR and switch to read-only mode after a fatal error happened like a write I/O errors of all mirrors. In such situations, on unmount, the superblock is written in btrfs_error_commit_super(). This is done with the intention to be able to evaluate the error flag on the next mount. A warning is printed in this case during the next mount and the log tree is ignored. The issue is that it is possible that the superblock points to a root that was not written (due to write I/O errors). The result is that the filesystem cannot be mounted. btrfsck also does not start and all the other btrfs-progs tools fail to start as well. However, mount -o recovery is working well and does the right things to recover the filesystem (i.e., don't use the log root, clear the free space cache and use the next mountable root that is stored in the root backup array). This patch removes the writing of the superblock when BTRFS_SUPER_FLAG_ERROR is set, and removes the handling of the error flag in the mount function. These lines can be used to reproduce the issue (using /dev/sdm): SCRATCH_DEV=/dev/sdm SCRATCH_MNT=/mnt echo 0 25165824 linear $SCRATCH_DEV 0 | dmsetup create foo ls -alLF /dev/mapper/foo mkfs.btrfs /dev/mapper/foo mount /dev/mapper/foo $SCRATCH_MNT echo bar > $SCRATCH_MNT/foo sync echo 0 25165824 error | dmsetup reload foo dmsetup resume foo ls -alF $SCRATCH_MNT touch $SCRATCH_MNT/1 ls -alF $SCRATCH_MNT sleep 35 echo 0 25165824 linear $SCRATCH_DEV 0 | dmsetup reload foo dmsetup resume foo sleep 1 umount $SCRATCH_MNT btrfsck /dev/mapper/foo dmsetup remove foo Signed-off-by:Stefan Behrens <sbehrens@giantdisaster.de> Signed-off-by: