Vitaly,
That's a good find. This is certainly the correct way to prevent soft lockup.
Will checkin.
Thanks.
-Amit
On Tuesday 22 August 2006 19:07, Vitaly Wool wrote:
> Hello folks,
>
> here's what I've got trying to debug with kgdb on powerpc target
> (Sandpoint) with the latest patches:
>
> BUG: soft lockup detected on CPU#0!
> Call Trace:
> [C028BCA0] [C0008428] show_stack+0x3c/0x194 (unreliable)
> [C028BCD0] [C00400E0] softlockup_tick+0x94/0xc4
> [C028BCF0] [C002858C] run_local_timers+0x18/0x28
> [C028BD00] [C00285CC] update_process_times+0x30/0x7c
> [C028BD10] [C000D0F0] timer_interrupt+0xd4/0x508
> [C028BD90] [C0010648] ret_from_except+0x0/0x14
> --- Exception: 901 at breakpoint+0xb4/0xcc
> LR = kgdb8250_interrupt+0x74/0xa8
> [C028BE50] [C0022FA4] irq_exit+0x48/0x58 (unreliable)
> [C028BE60] [C0131500] kgdb8250_interrupt+0x74/0xa8
> [C028BE70] [C004041C] handle_IRQ_event+0x64/0xb8
> [C028BE90] [C0041D94] handle_level_irq+0x9c/0x13c
> [C028BEB0] [C0018008] sandpoint_8259_cascade+0x7c/0xb0
> [C028BED0] [C0005F00] do_IRQ+0x9c/0xc0
> [C028BEE0] [C0010648] ret_from_except+0x0/0x14
> --- Exception: 501 at cpu_idle+0x48/0xe8
> LR = cpu_idle+0xd8/0xe8
> [C028BFB0] [C0003F8C] rest_init+0x28/0x38
> [C028BFC0] [C02336B0] start_kernel+0x1b8/0x220
> [C028BFF0] [00003860] 0x3860
>
> I've been poking around that a bit, and the problem seems to be introduced
> by core.patch. The old (working) version of core.patch did the following:
>
> void do_timer(struct pt_regs *regs)
> {
> + int this_cpu = smp_processor_id();
> jiffies_64++;
> /* prevent loading jiffies before storing new jiffies_64 value. */
> barrier();
> update_times();
> - softlockup_tick(regs);
> +
> +#ifdef CONFIG_KGDB
> + if(!atomic_read(&kgdb_sync_softlockup[this_cpu]))
> +#endif
> + softlockup_tick(regs);
> +
> }
>
> whereas the new one does the following:
>
> void do_timer(struct pt_regs *regs)
> {
> + int this_cpu = smp_processor_id();
> jiffies_64++;
> /* prevent loading jiffies before storing new jiffies_64 value. */
> barrier();
> update_times();
> +
> +#ifdef CONFIG_KGDB
> + if(!atomic_read(&kgdb_sync_softlockup[this_cpu]))
> +#endif
> + softlockup_tick();
> }
>
> which of course isn't equivalent.
>
> AFAICS, softlockup_tick() has moved to run_local_timers() so the current
> core.patch introduces second (wrong) softlockup_tick() call and doesn't
> modify the first one not to happen when kgdb_sync_softlockup is set. The
> latter one was triggering the soft lockup message I've been getting.
>
> So, please find the fix for core.patch as I see it inlined below, any
> comments are welcome.
>
> Vitaly
>
> kernel/timer.c | 10 ++++------
> 1 file changed, 4 insertions(+), 6 deletions(-)
>
> Signed-off-by: Vitaly Wool <[EMAIL PROTECTED]>
>
> diff -u linux-2.6.git/kernel/timer.c powerpc.git/kernel/timer.c
> --- linux-2.6.git/kernel/timer.c 2006-08-11 19:55:59.000000000 +0400
> +++ powerpc.git/kernel/timer.c
> @@ -1258,7 +1258,11 @@
> */
> void run_local_timers(void)
> {
> + int this_cpu = smp_processor_id();
> raise_softirq(TIMER_SOFTIRQ);
> +#ifdef CONFIG_KGDB
> + if(!atomic_read(&kgdb_sync_softlockup[this_cpu]))
> +#endif
> softlockup_tick();
> }
>
> @@ -1284,16 +1288,10 @@
>
> void do_timer(struct pt_regs *regs)
> {
> - int this_cpu = smp_processor_id();
> jiffies_64++;
> /* prevent loading jiffies before storing new jiffies_64 value. */
> barrier();
> update_times();
> -
> -#ifdef CONFIG_KGDB
> - if(!atomic_read(&kgdb_sync_softlockup[this_cpu]))
> -#endif
> - softlockup_tick();
> }
>
> #ifdef __ARCH_WANT_SYS_ALARM
>
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