Fix the hand after the immediate reboot when the following command
sequence is performed on UFS SU+J rootfs:
cp -Rp /sbin/init /sbin/init.old
mv -f /sbin/init.old /sbin/init
Hang occurs on the rootfs unmount. There are two issues:
- Removed init binary, which is still mapped, creates a reference to
the removed vnode. The inodeblock for such vnode must have active
inodedep, which is (eventually) linked through the unlinked list. This
means that ffs_sync(MNT_SUSPEND) cannot succeed, because number of
softdep workitems for the mp is always > 0. FFS is suspended during
unmount, so unmount just hangs.
- As noted above, the inodedep is linked eventually. It is not
linked until the superblock is written. But at the vfs_unmountall()
time, when the rootfs is unmounted, the call is made to
ffs_unmount()->ffs_sync() before vflush(), and ffs_sync() only calls
ffs_sbupdate() after all workitems are flushed. It is masked for
normal system operations, because syncer works in parallel and
eventually flushes superblock. Syncer is stopped when rootfs
unmounted, so ffs_sync() must do sb update on its own.
Correct the issues listed above. For MNT_SUSPEND, count the number of
linked unlinked inodedeps (this is not a typo) and substract the count
of such workitems from the total. For the second issue, the
ffs_sbupdate() is called right after device sync in ffs_sync() loop.
There is third problem, occuring with both SU and SU+J. The
softdep_waitidle() loop, which waits for softdep_flush() thread to
clear the worklist, only waits 20ms max. It seems that the 1 tick,
specified for msleep(9), was a typo.
Add fsync(devvp, MNT_WAIT) call to softdep_waitidle(), which seems to
significantly help the softdep thread, and change the MNT_LAZY update
at the reboot time to MNT_WAIT for similar reasons. Note that
userspace cannot create more work while devvp is flushed, since the
mount point is always suspended before the call to softdep_waitidle()
in unmount or remount path.
PR: 195458
In collaboration with: gjb, pho
Reviewed by: mckusick
Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks