RE: [PATCH v2] x86/nmi: Fix nmi_handle duration miscalculation

[Zhou, Libing (NSB - CN/Hangzhou)]

Hi,

Any comment on this?

-----Original Message-----
From: Libing Zhou <libing.zhou@xxxxxxxxxxxxxxx> 
Sent: 2020年8月20日 10:57
To: peterz@xxxxxxxxxxxxx; tglx@xxxxxxxxxxxxx; mingo@xxxxxxxxxx; bp@xxxxxxxxx; bp@xxxxxxx; x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx; Zhou, Libing (NSB - CN/Hangzhou) <libing.zhou@xxxxxxxxxxxxxxx>; hpa@xxxxxxxxx
Subject: [PATCH v2] x86/nmi: Fix nmi_handle duration miscalculation

In nmi_check_duration(), the 'whole_msecs' value get from 'action->max_duration' is wrong.

Fixes: 248ed51048c4 ("x86/nmi: Remove irq_work from the long duration NMI handler")
Signed-off-by: Libing Zhou <libing.zhou@xxxxxxxxxxxxxxx>
---
v2:
Change solution as peterz@xxxxxxxxxxxxx suggested.

 arch/x86/kernel/nmi.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c index 4fc9954a9560..47381666d6a5 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -102,7 +102,6 @@ fs_initcall(nmi_warning_debugfs);
 
 static void nmi_check_duration(struct nmiaction *action, u64 duration)  {
-	u64 whole_msecs = READ_ONCE(action->max_duration);
 	int remainder_ns, decimal_msecs;
 
 	if (duration < nmi_longest_ns || duration < action->max_duration) @@ -110,12 +109,12 @@ static void nmi_check_duration(struct nmiaction *action, u64 duration)
 
 	action->max_duration = duration;
 
-	remainder_ns = do_div(whole_msecs, (1000 * 1000));
+	remainder_ns = do_div(duration, (1000 * 1000));
 	decimal_msecs = remainder_ns / 1000;
 
 	printk_ratelimited(KERN_INFO
 		"INFO: NMI handler (%ps) took too long to run: %lld.%03d msecs\n",
-		action->handler, whole_msecs, decimal_msecs);
+		action->handler, duration, decimal_msecs);
 }
 
 static int nmi_handle(unsigned int type, struct pt_regs *regs)
--
2.22.0