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lockd: don't depend on lockd main loop to end grace

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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>
This commit is contained in:
J. Bruce Fields 2008-03-18 19:00:19 -04:00
parent 8fafa90082
commit c8ab5f2a13
1 changed files with 15 additions and 13 deletions
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28
fs/lockd/svc.c
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@ -97,17 +97,22 @@ unsigned long get_nfs_grace_period(void)
}
EXPORT_SYMBOL(get_nfs_grace_period);
static unsigned long set_grace_period(void)
{
nlmsvc_grace_period = 1;
return get_nfs_grace_period() + jiffies;
}
static inline void clear_grace_period(void)
static void grace_ender(struct work_struct *not_used)
{
nlmsvc_grace_period = 0;
}
static DECLARE_DELAYED_WORK(grace_period_end, grace_ender);
static void set_grace_period(void)
{
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);
}
/*
* This is the lockd kernel thread
*/
@ -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();