linux-kernel - Re: [UNTESTED PATCH] x86, mce: Avoid double entry of deferred errors into the genpool.

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Date:	Thu, 19 Nov 2015 17:15:21 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Tony Luck <tony.luck@...el.com>
Cc:	"Chen, Gong" <gong.chen@...ux.intel.com>,
	linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [UNTESTED PATCH] x86, mce: Avoid double entry of deferred errors
 into the genpool.

On Wed, Nov 11, 2015 at 02:01:51PM -0800, Tony Luck wrote:
> We used to have a special ring buffer for deferred errors that
> was used to mark problem pages. We replaced that with a genpool.
> Then later converted mce_log() to also use the same genpool. As
> a result we end up adding all deferred errors to the genpool twice.
> 
> Rearrange this code. Make sure to set the m.severity and m.usable_addr
> fields for deferred errors. Then if flags and mca_cfg.dont_log_ce mean
> we call mce_log() we are done, because that will add this entry to the
> genpool.
> 
> If we skipped mce_log(), then we still want to take action for the
> deferred error, so add to the genpool.
> 
> Changed the name of the boolean "error_logged" to "error_seen", we
> should set it whether of not we logged an error because the return
> value from machine_check_poll() is used to decide whether storms
> have subsided or not.
> 
> Reported-by: Chen, Gong <gong.chen.linux.intel.com>
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>  arch/x86/kernel/cpu/mcheck/mce.c | 24 +++++++++++++-----------
>  1 file changed, 13 insertions(+), 11 deletions(-)

Applied, thanks.

Btw, looking at that mce.usable_addr, it doesn't make a whole lotta
sense to me and we can use mce_usable_address() directly instead and use
the byte in struct mce for something more important. So how about I kill
it (diff ontop of yours):

---
diff --git a/arch/x86/include/uapi/asm/mce.h b/arch/x86/include/uapi/asm/mce.h
index 03429da2fa80..2184943341bf 100644
--- a/arch/x86/include/uapi/asm/mce.h
+++ b/arch/x86/include/uapi/asm/mce.h
@@ -16,7 +16,7 @@ struct mce {
 	__u8  cpuvendor;	/* cpu vendor as encoded in system.h */
 	__u8  inject_flags;	/* software inject flags */
 	__u8  severity;
-	__u8  usable_addr;
+	__u8  pad;
 	__u32 cpuid;	/* CPUID 1 EAX */
 	__u8  cs;		/* code segment */
 	__u8  bank;	/* machine check bank */
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 6531cb46803c..fb8b1db7b150 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -484,7 +484,7 @@ static int srao_decode_notifier(struct notifier_block *nb, unsigned long val,
 	if (!mce)
 		return NOTIFY_DONE;
 
-	if (mce->usable_addr && (mce->severity == MCE_AO_SEVERITY)) {
+	if (mce_usable_address(mce) && (mce->severity == MCE_AO_SEVERITY)) {
 		pfn = mce->addr >> PAGE_SHIFT;
 		memory_failure(pfn, MCE_VECTOR, 0);
 	}
@@ -610,12 +610,9 @@ bool machine_check_poll(enum mcp_flags flags, mce_banks_t *b)
 
 		severity = mce_severity(&m, mca_cfg.tolerant, NULL, false);
 
-		if (severity == MCE_DEFERRED_SEVERITY && memory_error(&m)) {
-			if (m.status & MCI_STATUS_ADDRV) {
+		if (severity == MCE_DEFERRED_SEVERITY && memory_error(&m))
+			if (m.status & MCI_STATUS_ADDRV)
 				m.severity = severity;
-				m.usable_addr = mce_usable_address(&m);
-			}
-		}
 
 		/*
 		 * Don't get the IP here because it's unlikely to
@@ -623,7 +620,7 @@ bool machine_check_poll(enum mcp_flags flags, mce_banks_t *b)
 		 */
 		if (!(flags & MCP_DONTLOG) && !mca_cfg.dont_log_ce)
 			mce_log(&m);
-		else if (m.usable_addr) {
+		else if (mce_usable_address(&m)) {
 			/*
 			 * Although we skipped logging this, we still want
 			 * to take action. Add to the pool so the registered
@@ -1091,7 +1088,6 @@ void do_machine_check(struct pt_regs *regs, long error_code)
 
 		/* assuming valid severity level != 0 */
 		m.severity = severity;
-		m.usable_addr = mce_usable_address(&m);
 
 		mce_log(&m);
 
-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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