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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: 1. 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. 2. 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
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