lkml.org 
[lkml]   [2014]   [Jul]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH 4/6] x86-mce: Add spinlocks to prevent duplicated MCP and CMCI reports.
On Thu, Jul 10, 2014 at 09:12:24PM +0200, Borislav Petkov wrote:
> I'll think about it more tomorrow - my brain is twisted enough for
> today. :-)

Ok, new day, new luck. :-)

So, following yesterday's discussion, our problem is IMHO that shared
banks could be read multiple times before they're finally cleared,
leading to repeated MCE records.

Now, staring at machine_check_poll, the processing is controlled by one
bit - MCI_STATUS_VAL - which decides what happens next.

So how about we change processing around this one bit: we let only one
reader access MSR_IA32_MCx_STATUS(i) and clear it right afterwards by
saving its contents to m.status previously.

Concurrent callers of machine_check_poll will not read the MCI_STATUS
MSR and since they look at the local copy m.status which is 0, they'll
go to the next bank.

And this for the cost of a locked CMPXCHG when we have to inc
poll_reader which should be cheaper than disabling IRQs everytime.

I.e., something like that. Hmm...

---
diff --git a/arch/x86/kernel/cpu/mcheck/mce-internal.h b/arch/x86/kernel/cpu/mcheck/mce-internal.h
index 09edd0b65fef..5483b507025a 100644
--- a/arch/x86/kernel/cpu/mcheck/mce-internal.h
+++ b/arch/x86/kernel/cpu/mcheck/mce-internal.h
@@ -19,6 +19,7 @@ struct mce_bank {
unsigned char init; /* initialise bank? */
struct device_attribute attr; /* device attribute */
char attrname[ATTR_LEN]; /* attribute name */
+ atomic_t poll_reader; /* sync for polled shared banks */
};

int mce_severity(struct mce *a, int tolerant, char **msg);
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index bb92f38153b2..443861da86e4 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -609,9 +609,20 @@ void machine_check_poll(enum mcp_flags flags, mce_banks_t *b)
m.addr = 0;
m.bank = i;
m.tsc = 0;
+ m.status = 0;

barrier();
- m.status = mce_rdmsrl(MSR_IA32_MCx_STATUS(i));
+
+ if (atomic_add_unless(&mce_banks[i].poll_reader, 1, 1)) {
+ m.status = mce_rdmsrl(MSR_IA32_MCx_STATUS(i));
+
+ if (m.status & MCI_STATUS_VAL)
+ /* clear status register for this bank */
+ mce_wrmsrl(MSR_IA32_MCx_STATUS(i), 0);
+
+ atomic_dec(&mce_banks[i].poll_reader);
+ }
+
if (!(m.status & MCI_STATUS_VAL))
continue;

@@ -637,17 +648,12 @@ void machine_check_poll(enum mcp_flags flags, mce_banks_t *b)
if (!(flags & MCP_DONTLOG) && !mca_cfg.dont_log_ce)
mce_log(&m);

- /*
- * Clear state for this bank.
- */
- mce_wrmsrl(MSR_IA32_MCx_STATUS(i), 0);
}

/*
* Don't clear MCG_STATUS here because it's only defined for
* exceptions.
*/
-
sync_core();
}
EXPORT_SYMBOL_GPL(machine_check_poll);


--
Regards/Gruss,
Boris.

Sent from a fat crate under my desk. Formatting is fine.
--


\
 
 \ /
  Last update: 2014-07-11 12:01    [W:0.077 / U:4.084 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site