From c8ab5f2a13fb41a878863c61a1e27d78f1844b5e Mon Sep 17 00:00:00 2001 From: "J. Bruce Fields" Date: Tue, 18 Mar 2008 19:00:19 -0400 Subject: 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 and myself." Signed-off-by: J. Bruce Fields Cc: Nakano Hiroaki Cc: Itsuro Oda --- fs/lockd/svc.c | 24 +++++++++++++----------- 1 file changed, 13 insertions(+), 11 deletions(-) (limited to 'fs/lockd') diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c index bdc607bb25e9..f345ef7fb8ae 100644 --- a/fs/lockd/svc.c +++ b/fs/lockd/svc.c @@ -97,15 +97,20 @@ 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; + cancel_delayed_work_sync(&grace_period_end); + schedule_delayed_work(&grace_period_end, grace_period); } /* @@ -116,7 +121,6 @@ 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 +143,7 @@ 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 +157,13 @@ 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 +190,7 @@ 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(); -- cgit v1.2.3