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Subject[PATCH 2/2] lockd: don't depend on lockd main loop to end grace
Date
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>
---
fs/lockd/svc.c | 23 ++++++++++++-----------
1 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
index bdc607b..450a3fa 100644
--- a/fs/lockd/svc.c
+++ b/fs/lockd/svc.c
@@ -97,15 +97,19 @@ unsigned long get_nfs_grace_period(void)
}
EXPORT_SYMBOL(get_nfs_grace_period);

-static unsigned long set_grace_period(void)
+static void grace_ender(struct work_struct *not_used)
{
- nlmsvc_grace_period = 1;
- return get_nfs_grace_period() + jiffies;
+ nlmsvc_grace_period = 0;
}

-static inline void clear_grace_period(void)
+static DECLARE_DELAYED_WORK(grace_period_end, grace_ender);
+
+static void set_grace_period(void)
{
- nlmsvc_grace_period = 0;
+ unsigned long grace_period = get_nfs_grace_period() + jiffies;
+
+ nlmsvc_grace_period = 1;
+ schedule_delayed_work(&grace_period_end, grace_period);
}

/*
@@ -116,7 +120,6 @@ lockd(void *vrqstp)
{
int err = 0, preverr = 0;
struct svc_rqst *rqstp = vrqstp;
- unsigned long grace_period_expire;

/* try_to_freeze() is called from svc_recv() */
set_freezable();
@@ -139,7 +142,7 @@ lockd(void *vrqstp)
nlm_timeout = LOCKD_DFLT_TIMEO;
nlmsvc_timeout = nlm_timeout * HZ;

- grace_period_expire = set_grace_period();
+ set_grace_period();

/*
* The main request loop. We don't terminate until the last
@@ -153,16 +156,13 @@ lockd(void *vrqstp)
flush_signals(current);
if (nlmsvc_ops) {
nlmsvc_invalidate_all();
- grace_period_expire = set_grace_period();
+ set_grace_period();
}
continue;
}

timeout = nlmsvc_retry_blocked();

- if (time_before(grace_period_expire, jiffies))
- clear_grace_period();
-
/*
* Find a socket with data available and call its
* recvfrom routine.
@@ -189,6 +189,7 @@ lockd(void *vrqstp)
svc_process(rqstp);
}
flush_signals(current);
+ cancel_delayed_work_sync(&grace_period_end);
if (nlmsvc_ops)
nlmsvc_invalidate_all();
nlm_shutdown_hosts();
--
1.5.5.rc1


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