From: Thomas Gleixner Date: Tue, 3 Jul 2007 18:05:20 +0000 (+0200) Subject: NTP: remove clock_was_set() call to prevent deadlock X-Git-Tag: v2.6.22~36 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=746976a301ac9c9aa10d7d42454f8d6cdad8ff2b;p=linux-2.6 NTP: remove clock_was_set() call to prevent deadlock The clock_was_set() call in seconds_overflow() which happens only when leap seconds are inserted / deleted is wrong in two aspects: 1. it results in a call to on_each_cpu() with interrupts disabled 2. it is potential deadlock source vs. call_lock in smp_call_function() The only possible side effect of the removal might be, that an absolute CLOCK_REALTIME timer fires 1 second too late, in the rare case of leap second deletion and an absolute CLOCK_REALTIME timer which expires in the affected time frame. It will never fire too early. This was probably observed by the reporter of a June 30th -> July 1st hang: http://lkml.org/lkml/2007/7/3/103 A similar problem was observed by Dave Jones, who provided a screen shot with a lockdep back trace, which allowed to analyse the problem. Signed-off-by: Thomas Gleixner Acked-by: Ingo Molnar Signed-off-by: Linus Torvalds --- diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c index 87aa5ff931..cf53bb5814 100644 --- a/kernel/time/ntp.c +++ b/kernel/time/ntp.c @@ -122,7 +122,6 @@ void second_overflow(void) */ time_interpolator_update(-NSEC_PER_SEC); time_state = TIME_OOP; - clock_was_set(); printk(KERN_NOTICE "Clock: inserting leap second " "23:59:60 UTC\n"); } @@ -137,7 +136,6 @@ void second_overflow(void) */ time_interpolator_update(NSEC_PER_SEC); time_state = TIME_WAIT; - clock_was_set(); printk(KERN_NOTICE "Clock: deleting leap second " "23:59:59 UTC\n"); }