Messages in this thread Patch in this message | | | Date | Fri, 9 Jan 2009 14:31:10 -0600 | From | Chris Adams <> | Subject | [PATCH] Fix leap second message hang |
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Resending this outside the big long thread to make sure it gets added (it isn't critical right now but I don't want to forget it).
From: Chris Adams <cmadams@hiwaay.net>
The code to handle leap seconds printks an information message when the second is inserted or deleted. It does this while holding xtime_lock. However, printk wakes up klogd, and in some cases, the scheduler tries to get the current kernel time, trying to get xtime_lock (which results in a deadlock). This moved the printks outside of the lock. It also adds a comment to not use printk while holding xtime_lock.
Signed-off-by: Chris Adams <cmadams@hiwaay.net> Acked-by: Linas Vepstas <linasvepstas@gmail.com> --- diff -urpN linux-2.6.28-git5-vanilla/include/linux/time.h linux-2.6.28-git5/include/linux/time.h --- linux-2.6.28-git5-vanilla/include/linux/time.h 2009-01-02 22:09:10.000000000 -0600 +++ linux-2.6.28-git5/include/linux/time.h 2009-01-03 11:57:27.000000000 -0600 @@ -99,6 +99,12 @@ static inline struct timespec timespec_s extern struct timespec xtime; extern struct timespec wall_to_monotonic; + +/* + * Do not call printk while holding this lock; it wakes klogd and the + * scheduler may try to get the current kernel time, which will try to get + * this lock. + */ extern seqlock_t xtime_lock; extern unsigned long read_persistent_clock(void); diff -urpN linux-2.6.28-git5-vanilla/kernel/time/ntp.c linux-2.6.28-git5/kernel/time/ntp.c --- linux-2.6.28-git5-vanilla/kernel/time/ntp.c 2009-01-02 22:09:34.000000000 -0600 +++ linux-2.6.28-git5/kernel/time/ntp.c 2009-01-03 11:57:46.000000000 -0600 @@ -130,6 +130,7 @@ void ntp_clear(void) static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer) { enum hrtimer_restart res = HRTIMER_NORESTART; + const char *msg = NULL; write_seqlock(&xtime_lock); @@ -140,8 +141,7 @@ static enum hrtimer_restart ntp_leap_sec xtime.tv_sec--; wall_to_monotonic.tv_sec++; time_state = TIME_OOP; - printk(KERN_NOTICE "Clock: " - "inserting leap second 23:59:60 UTC\n"); + msg = "Clock: inserting leap second 23:59:60 UTC"; hrtimer_add_expires_ns(&leap_timer, NSEC_PER_SEC); res = HRTIMER_RESTART; break; @@ -150,8 +150,7 @@ static enum hrtimer_restart ntp_leap_sec time_tai--; wall_to_monotonic.tv_sec--; time_state = TIME_WAIT; - printk(KERN_NOTICE "Clock: " - "deleting leap second 23:59:59 UTC\n"); + msg = "Clock: deleting leap second 23:59:59 UTC"; break; case TIME_OOP: time_tai++; @@ -166,6 +165,9 @@ static enum hrtimer_restart ntp_leap_sec write_sequnlock(&xtime_lock); + if (msg) + printk(KERN_NOTICE "%s\n", msg); + return res; }
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