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SubjectRe: [PATCH v4 2/2] x86 mce: use new printk recursion disabling interface
On Mon, 04 Jun 2012 11:07:11 +0800
ShuoX Liu <shuox.liu@intel.com> wrote:

> From: ShuoX Liu <shuox.liu@intel.com>
>
> Disable printk recursion to make sure MCE logs printed out.
>
> Signed-off-by: Yanmin Zhang <yanmin_zhang@linux.intel.com>
> Signed-off-by: ShuoX Liu <shuox.liu@intel.com>
> ---
> We hit it when running a MTBF testing on a Android atom mobile.
> ---
> arch/x86/kernel/cpu/mcheck/mce.c | 2 ++
> 1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> index 2afcbd2..906e838 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -306,6 +306,7 @@ static void mce_panic(char *msg, struct mce *final, char *exp)
> {
> int i, apei_err = 0;
>
> + printk_recursion_check_disable();
> if (!fake_panic) {
> /*
> * Make sure only one CPU runs in machine check panic
> @@ -360,6 +361,7 @@ static void mce_panic(char *msg, struct mce *final, char *exp)
> panic(msg);
> } else
> pr_emerg(HW_ERR "Fake kernel panic: %s\n", msg);
> + printk_recursion_check_enable();
> }
>
> /* Support code for software error injection */

A couple of things here.

a) mce_panic() has a "return" statement deep inside. So we return
from mce_panic() with the recursion check disabled. whoops.

b) adding a nice comment is nice.

--- a/arch/x86/kernel/cpu/mcheck/mce.c~x86-mce-use-new-printk-recursion-disabling-interface-fix
+++ a/arch/x86/kernel/cpu/mcheck/mce.c
@@ -303,11 +303,10 @@ static void wait_for_panic(void)
panic("Panicing machine check CPU died");
}

-static void mce_panic(char *msg, struct mce *final, char *exp)
+static void __mce_panic(char *msg, struct mce *final, char *exp)
{
int i, apei_err = 0;

- printk_recursion_check_disable();
if (!fake_panic) {
/*
* Make sure only one CPU runs in machine check panic
@@ -362,6 +361,17 @@ static void mce_panic(char *msg, struct
panic(msg);
} else
pr_emerg(HW_ERR "Fake kernel panic: %s\n", msg);
+}
+
+/*
+ * If an MCE happens to occur during the execution of a printk(), we want the
+ * MCE information to be displayed. But printk()'s recursion checking prevents
+ * that. So temporarily disable it.
+ */
+static void mce_panic(char *msg, struct mce *final, char *exp)
+{
+ printk_recursion_check_disable();
+ __mce_panic(msg, final, exp);
printk_recursion_check_enable();
}

_


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