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27 March 2024, 02:37:15 UTC
Revision b37199e626b31e1175fb06764c5d1d687723aac2 authored by Al Viro on 20 March 2014, 19:18:22 UTC, committed by Al Viro on 23 March 2014, 04:32:55 UTC 
rcuwalk: recheck mount_lock after mountpoint crossing attempts
 
We can get false negative from __lookup_mnt() if an unrelated vfsmount
gets moved.  In that case legitimize_mnt() is guaranteed to fail,
and we will fall back to non-RCU walk... unless we end up running
into a hard error on a filesystem object we wouldn't have reached
if not for that false negative.  IOW, delaying that check until
the end of pathname resolution is wrong - we should recheck right
after we attempt to cross the mountpoint.  We don't need to recheck
unless we see d_mountpoint() being true - in that case even if
we have just raced with mount/umount, we can simply go on as if
we'd come at the moment when the sucker wasn't a mountpoint; if we
run into a hard error as the result, it was a legitimate outcome.
__lookup_mnt() returning NULL is different in that respect, since
it might've happened due to operation on completely unrelated
mountpoint.

Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
1 parent e825196
History
Tip revision: b37199e626b31e1175fb06764c5d1d687723aac2 authored by Al Viro on 20 March 2014, 19:18:22 UTC
rcuwalk: recheck mount_lock after mountpoint crossing attempts
Tip revision: b37199e
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