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>

8 files changed, 28 insertions, 33 deletions

diff --git a/arch/alpha/kernel/time.c b/arch/alpha/kernel/time.c
index 1dd50d07693c..75480cab0893 100644
--- a/arch/alpha/kernel/time.c
+++ b/arch/alpha/kernel/time.c
@@ -119,13 +119,8 @@ irqreturn_t timer_interrupt(int irq, void *dev)
         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 @@ irqreturn_t timer_interrupt(int irq, void *dev)
         }
 
         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 5bd64e341df3..9bdc8f99183a 100644
--- a/arch/blackfin/kernel/time.c
+++ b/arch/blackfin/kernel/time.c
@@ -137,9 +137,6 @@ irqreturn_t timer_interrupt(int irq, void *dummy)
 
         do_timer(1);
 
-#ifndef CONFIG_SMP
-        update_process_times(user_mode(get_irq_regs()));
-#endif
         profile_tick(CPU_PROFILING);
 
         /*
@@ -161,6 +158,11 @@ irqreturn_t timer_interrupt(int irq, void *dummy)
                         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 925fb0199a0f..69f6a4ef5d61 100644
--- a/arch/frv/kernel/time.c
+++ b/arch/frv/kernel/time.c
@@ -63,6 +63,7 @@ static irqreturn_t timer_interrupt(int irq, void *dummy)
         /* 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 @@ static irqreturn_t timer_interrupt(int irq, void *dummy)
         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 @@ static irqreturn_t timer_interrupt(int irq, void *dummy)
 #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 89cdbcaeb45f..0ccfb2ad6380 100644
--- a/arch/m68knommu/kernel/time.c
+++ b/arch/m68knommu/kernel/time.c
@@ -42,14 +42,12 @@ irqreturn_t arch_timer_interrupt(int irq, void *dummy)
         /* 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 @@ irqreturn_t arch_timer_interrupt(int irq, void *dummy)
         }
 
         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 499e07beebe2..71312324b5de 100644
--- a/arch/sh/kernel/timers/timer-cmt.c
+++ b/arch/sh/kernel/timers/timer-cmt.c
@@ -100,16 +100,7 @@ static irqreturn_t cmt_timer_interrupt(int irq, void *dev_id)
         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 b7499a2a9188..463cd08f9517 100644
--- a/arch/sh/kernel/timers/timer-mtu2.c
+++ b/arch/sh/kernel/timers/timer-mtu2.c
@@ -100,9 +100,7 @@ static irqreturn_t mtu2_timer_interrupt(int irq, void *dev_id)
         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 4cd5d7818dc6..a6a6f9823370 100644
--- a/arch/sparc/kernel/pcic.c
+++ b/arch/sparc/kernel/pcic.c
@@ -713,10 +713,10 @@ static irqreturn_t pcic_timer_handler (int irq, void *h)
         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 00b393c3a4a0..cfaf22c05bc4 100644
--- a/arch/sparc/kernel/time.c
+++ b/arch/sparc/kernel/time.c
@@ -128,10 +128,6 @@ irqreturn_t timer_interrupt(int irq, void *dev_id)
         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 @@ irqreturn_t timer_interrupt(int irq, void *dev_id)
         }
         write_sequnlock(&xtime_lock);
 
+#ifndef CONFIG_SMP
+        update_process_times(user_mode(get_irq_regs()));
+#endif
         return IRQ_HANDLED;
 }