Messages in this thread Patch in this message | | | Date | Wed, 26 Aug 2009 14:00:01 +0900 | From | Fernando Luis Vázquez Cao <> | Subject | [RFC, PATCH] filesystem freeze: fix sys_umount induced perpetual freeze |
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The current locking scheme for filesystem freeze avoids races between freeze_bdev() and do_umount() by taking the s_umount semaphore.
If freeze_bdev() wins the race the process that invoked sys_umount will sleep until thaw_bdev releases the semaphore. Unfortunately, this will never happen because thaw_bdev bails out early the bd_fsfreeze_count check having failed (the count is 0).
The problem is that the block_device that ioctl_fsthaw() passes to thaw_bdev() is not the one that we freezed because before sleeping in deactivate_super() do_umount() released the dentry (dput()) and freed the vfs mount (free_vfsmnt()).
This patch works around this issue by checking the freeze level in do_umount().
Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp> ---
diff -urNp linux-2.6.31-rc7-orig/fs/namespace.c linux-2.6.31-rc7/fs/namespace.c --- linux-2.6.31-rc7-orig/fs/namespace.c 2009-08-25 16:39:46.000000000 +0900 +++ linux-2.6.31-rc7/fs/namespace.c 2009-08-26 11:30:10.000000000 +0900 @@ -1033,6 +1033,8 @@ static int do_umount(struct vfsmount *mn if (retval) return retval;
+ vfs_check_frozen(sb, SB_FREEZE_WRITE); + /* * Allow userspace to request a mountpoint be expired rather than * unmounting unconditionally. Unmount only happens if:
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