xtime_lock vs update_process_times
Commit d3d74453c34f8fd87674a8cf5b8a327c68f22e99 ("hrtimer: fixup the
HRTIMER_CB_IRQSAFE_NO_SOFTIRQ fallback") broke several archs, and since
only Russell bothered to merge the fix, and Greg to ACK his arch, I'm
sending this for merger.
I have confirmation that the Alpha bit results in a booting kernel.
That leaves: blackfin, frv, sh and sparc untested.
The deadlock in question was found by Russell:
IRQ handle
-> timer_tick() - xtime seqlock held for write
-> update_process_times()
-> run_local_timers()
-> hrtimer_run_queues()
-> hrtimer_get_softirq_time() - tries to get a read lock
Now, Thomas assures me the fix is trivial, only do_timer() needs to be
done under the xtime_lock, and update_process_times() can savely be
removed from under it.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Greg Ungerer <gerg@uclinux.org>
CC: Richard Henderson <rth@twiddle.net>
CC: Bryan Wu <bryan.wu@analog.com>
CC: David Howells <dhowells@redhat.com>
CC: Paul Mundt <lethal@linux-sh.org>
CC: William Irwin <wli@holomorphy.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/alpha/kernel/time.c b/arch/alpha/kernel/time.c
index 1dd50d0..75480ca 100644
--- a/arch/alpha/kernel/time.c
+++ b/arch/alpha/kernel/time.c
@@ -119,13 +119,8 @@
state.partial_tick = delta & ((1UL << FIX_SHIFT) - 1);
nticks = delta >> FIX_SHIFT;
- while (nticks > 0) {
- do_timer(1);
-#ifndef CONFIG_SMP
- update_process_times(user_mode(get_irq_regs()));
-#endif
- nticks--;
- }
+ if (nticks)
+ do_timer(nticks);
/*
* If we have an externally synchronized Linux clock, then update
@@ -141,6 +136,12 @@
}
write_sequnlock(&xtime_lock);
+
+#ifndef CONFIG_SMP
+ while (nticks--)
+ update_process_times(user_mode(get_irq_regs()));
+#endif
+
return IRQ_HANDLED;
}
diff --git a/arch/blackfin/kernel/time.c b/arch/blackfin/kernel/time.c
index 5bd64e3..9bdc8f9 100644
--- a/arch/blackfin/kernel/time.c
+++ b/arch/blackfin/kernel/time.c
@@ -137,9 +137,6 @@
do_timer(1);
-#ifndef CONFIG_SMP
- update_process_times(user_mode(get_irq_regs()));
-#endif
profile_tick(CPU_PROFILING);
/*
@@ -161,6 +158,11 @@
last_rtc_update = xtime.tv_sec - 600;
}
write_sequnlock(&xtime_lock);
+
+#ifndef CONFIG_SMP
+ update_process_times(user_mode(get_irq_regs()));
+#endif
+
return IRQ_HANDLED;
}
diff --git a/arch/frv/kernel/time.c b/arch/frv/kernel/time.c
index 925fb01..69f6a4e 100644
--- a/arch/frv/kernel/time.c
+++ b/arch/frv/kernel/time.c
@@ -63,6 +63,7 @@
/* last time the cmos clock got updated */
static long last_rtc_update = 0;
+ profile_tick(CPU_PROFILING);
/*
* Here we are in the timer irq handler. We just have irqs locally
* disabled but we don't know if the timer_bh is running on the other
@@ -73,8 +74,6 @@
write_seqlock(&xtime_lock);
do_timer(1);
- update_process_times(user_mode(get_irq_regs()));
- profile_tick(CPU_PROFILING);
/*
* If we have an externally synchronized Linux clock, then update
@@ -99,6 +98,9 @@
#endif /* CONFIG_HEARTBEAT */
write_sequnlock(&xtime_lock);
+
+ update_process_times(user_mode(get_irq_regs()));
+
return IRQ_HANDLED;
}
diff --git a/arch/m68knommu/kernel/time.c b/arch/m68knommu/kernel/time.c
index 89cdbca..0ccfb2a 100644
--- a/arch/m68knommu/kernel/time.c
+++ b/arch/m68knommu/kernel/time.c
@@ -42,14 +42,12 @@
/* last time the cmos clock got updated */
static long last_rtc_update=0;
+ if (current->pid)
+ profile_tick(CPU_PROFILING);
+
write_seqlock(&xtime_lock);
do_timer(1);
-#ifndef CONFIG_SMP
- update_process_times(user_mode(get_irq_regs()));
-#endif
- if (current->pid)
- profile_tick(CPU_PROFILING);
/*
* If we have an externally synchronized Linux clock, then update
@@ -67,6 +65,10 @@
}
write_sequnlock(&xtime_lock);
+
+#ifndef CONFIG_SMP
+ update_process_times(user_mode(get_irq_regs()));
+#endif
return(IRQ_HANDLED);
}
diff --git a/arch/sh/kernel/timers/timer-cmt.c b/arch/sh/kernel/timers/timer-cmt.c
index 499e07b..7131232 100644
--- a/arch/sh/kernel/timers/timer-cmt.c
+++ b/arch/sh/kernel/timers/timer-cmt.c
@@ -100,16 +100,7 @@
timer_status &= ~0x80;
ctrl_outw(timer_status, CMT_CMCSR_0);
- /*
- * Here we are in the timer irq handler. We just have irqs locally
- * disabled but we don't know if the timer_bh is running on the other
- * CPU. We need to avoid to SMP race with it. NOTE: we don' t need
- * the irq version of write_lock because as just said we have irq
- * locally disabled. -arca
- */
- write_seqlock(&xtime_lock);
handle_timer_tick();
- write_sequnlock(&xtime_lock);
return IRQ_HANDLED;
}
diff --git a/arch/sh/kernel/timers/timer-mtu2.c b/arch/sh/kernel/timers/timer-mtu2.c
index b7499a2..463cd08 100644
--- a/arch/sh/kernel/timers/timer-mtu2.c
+++ b/arch/sh/kernel/timers/timer-mtu2.c
@@ -100,9 +100,7 @@
ctrl_outb(timer_status, MTU2_TSR_1);
/* Do timer tick */
- write_seqlock(&xtime_lock);
handle_timer_tick();
- write_sequnlock(&xtime_lock);
return IRQ_HANDLED;
}
diff --git a/arch/sparc/kernel/pcic.c b/arch/sparc/kernel/pcic.c
index 4cd5d78..a6a6f98 100644
--- a/arch/sparc/kernel/pcic.c
+++ b/arch/sparc/kernel/pcic.c
@@ -713,10 +713,10 @@
write_seqlock(&xtime_lock); /* Dummy, to show that we remember */
pcic_clear_clock_irq();
do_timer(1);
+ write_sequnlock(&xtime_lock);
#ifndef CONFIG_SMP
update_process_times(user_mode(get_irq_regs()));
#endif
- write_sequnlock(&xtime_lock);
return IRQ_HANDLED;
}
diff --git a/arch/sparc/kernel/time.c b/arch/sparc/kernel/time.c
index 00b393c..cfaf22c 100644
--- a/arch/sparc/kernel/time.c
+++ b/arch/sparc/kernel/time.c
@@ -128,10 +128,6 @@
clear_clock_irq();
do_timer(1);
-#ifndef CONFIG_SMP
- update_process_times(user_mode(get_irq_regs()));
-#endif
-
/* Determine when to update the Mostek clock. */
if (ntp_synced() &&
@@ -145,6 +141,9 @@
}
write_sequnlock(&xtime_lock);
+#ifndef CONFIG_SMP
+ update_process_times(user_mode(get_irq_regs()));
+#endif
return IRQ_HANDLED;
}
