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xfs: zero length symlinks are not valid
A log recovery failure has been reproduced where a symlink inode has a zero length in extent form. It was caused by a shutdown during a combined fstress+fsmark workload. The underlying problem is the issue in xfs_inactive_symlink(): the inode is unlocked between the symlink inactivation/truncation and the inode being freed. This opens a window for the inode to be written to disk before it xfs_ifree() removes it from the unlinked list, marks it free in the inobt and zeros the mode. For shortform inodes, the fix is simple. xfs_ifree() clears the data fork state, so there's no need to do it in xfs_inactive_symlink(). This means the shortform fork verifier will not see a zero length data fork as it mirrors the inode size through to xfs_ifree()), and hence if the inode gets written back and the fork verifiers are run they will still see a fork that matches the on-disk inode size. For extent form (remote) symlinks, it is a little more tricky. Here we explicitly set the inode size to zero, so the above race can lead to zero length symlinks on disk. Because the inode is unlinked at this point (i.e. on the unlinked list) and unreferenced, it can never be seen again by a user. Hence when we set the inode size to zeor, also change the type to S_IFREG. xfs_ifree() expects S_IFREG inodes to be of zero length, and so this avoids all the problems of zero length symlinks ever hitting the disk. It also avoids the problem of needing to handle zero length symlink inodes in log recovery to replay the extent free intents and the remaining deferops to free the extents the symlink used. Also add a couple of asserts to warn us if zero length symlinks end up in either the symlink create or inactivation paths. Signed-off-by:Dave Chinner <dchinner@redhat.com> Reviewed-by: