On 2015-05-11 10:48:32 Mon, Daniel Axtens wrote:
> Before 69111bac42f5 ("powerpc: Replace __get_cpu_var uses"), in
> save_mce_event, index got the value of mce_nest_count, and
> mce_nest_count was incremented *after* index was set.
>
> However, that patch changed the behaviour so that mce_nest count was
> incremented *before* setting index.
>
> This causes an off-by-one error, as get_mce_event sets index as
> mce_nest_count - 1 before reading mce_event. Thus get_mce_event reads
> bogus data, causing warnings like
> "Machine Check Exception, Unknown event version 0 !"
> and breaking MCEs handling.
>
> Restore the old behaviour and unbreak MCE handling by moving the
> increment to after index is set.
>
> The same broken change occured in machine_check_queue_event (which set
> a queue read by machine_check_process_queued_event). Fix that too,
> unbreaking printing of MCE information.
>
> Fixes: 69111bac42f5 ("powerpc: Replace __get_cpu_var uses")
> CC: stable@xxxxxxxxxxxxxxx
> CC: Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Daniel Axtens <dja@xxxxxxxxxx>
Acked-by: Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxxxxxxx>
> ---
> arch/powerpc/kernel/mce.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kernel/mce.c b/arch/powerpc/kernel/mce.c
> index 15c99b6..f774b64 100644
> --- a/arch/powerpc/kernel/mce.c
> +++ b/arch/powerpc/kernel/mce.c
> @@ -73,8 +73,9 @@ void save_mce_event(struct pt_regs *regs, long handled,
> uint64_t nip, uint64_t addr)
> {
> uint64_t srr1;
> - int index = __this_cpu_inc_return(mce_nest_count);
> + int index = __this_cpu_read(mce_nest_count);
> struct machine_check_event *mce = this_cpu_ptr(&mce_event[index]);
> + __this_cpu_inc(mce_nest_count);
>
> /*
> * Return if we don't have enough space to log mce event.
> @@ -184,7 +185,8 @@ void machine_check_queue_event(void)
> if (!get_mce_event(&evt, MCE_EVENT_RELEASE))
> return;
>
> - index = __this_cpu_inc_return(mce_queue_count);
> + index = __this_cpu_read(mce_queue_count);
> + __this_cpu_inc(mce_queue_count);
> /* If queue is full, just return for now. */
> if (index >= MAX_MC_EVT) {
> __this_cpu_dec(mce_queue_count);
> --
> 2.1.4
>
> _______________________________________________
> Linuxppc-dev mailing list
> Linuxppc-dev@xxxxxxxxxxxxxxxx
> https://lists.ozlabs.org/listinfo/linuxppc-dev
--
Mahesh J Salgaonkar
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