lockd: don't depend on lockd main loop to end grace
End lockd's grace period using schedule_delayed_work() instead of a
check on every pass through the main loop.
After a later patch, we'll depend on lockd to end its grace period even
if it's not currently handling requests; so it shouldn't depend on being
woken up from the main loop to do so.
Also, Nakano Hiroaki (who independently produced a similar patch)
noticed that the current behavior is buggy in the face of jiffies
wraparound:
"lockd uses time_before() to determine whether the grace period
has expired. This would seem to be enough to avoid timer
wrap-around issues, but, unfortunately, that is not the case.
The time_* family of comparison functions can be safely used to
compare jiffies relatively close in time, but they stop working
after approximately LONG_MAX/2 ticks. nfsd can suffer this
problem because the time_before() comparison in lockd() is not
performed until the first request comes in, which means that if
there is no lockd traffic for more than LONG_MAX/2 ticks we are
screwed.
"The implication of this is that once time_before() starts
misbehaving any attempt from a NFS client to execute fcntl()
will be received with a NLM_LCK_DENIED_GRACE_PERIOD message for
25 days (assuming HZ=1000). In other words, the 50 seconds grace
period could turn into a grace period of 50 days or more.
"Note: This bug was analyzed independently by Oda-san
<oda@valinux.co.jp> and myself."
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Cc: Nakano Hiroaki <nakano.hiroaki@oss.ntt.co.jp>
Cc: Itsuro Oda <oda@valinux.co.jp>
1 file changed