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 1dd50d07693cb9241ce1d064b589d5d4938c64ff..75480cab0893c391619e681bdc1ee6dd6adbf7ed 100644 (file)
--- 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 5bd64e341df39cb53c9f70b29229274a72a416c9..9bdc8f99183a5e66a215ffeec71440fbe48b7bf6 100644 (file)
--- 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 925fb0199a0f21cc8df27e2cbaf137b67a7a3d47..69f6a4ef5d61b35c67323a85485e1cebedff7a43 100644 (file)
--- 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 89cdbcaeb45f00e5a1b7e44a78d4e9389853b4dc..0ccfb2ad63800ee44e449847840885d02760a011 100644 (file)
--- 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 499e07beebe28f6df7ec85ea0d52f655e3e7de3a..71312324b5defb4383d4760ecfd12f196fd52b7e 100644 (file)
--- 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 b7499a2a9188b97f7b9d949961f35e7afd0c9d5e..463cd08f951742609088fb00195b0cff47bf3543 100644 (file)
--- 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 4cd5d7818dc6f0acff518ce0250a54809d96e81a..a6a6f9823370582d3b6ef0ff18206c6d072f719a 100644 (file)
--- 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 00b393c3a4a09edcde2b89e283c9642199c09670..cfaf22c05bc460aacf9c5c15a3f4ce907bc57e90 100644 (file)
--- 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;
 }