* Re: 2.5.64 and jiffies wrap
2003-03-07 13:05 2.5.64 and jiffies wrap Jens Axboe
@ 2003-03-07 12:15 ` Andrew Morton
2003-03-07 13:20 ` Jens Axboe
0 siblings, 1 reply; 3+ messages in thread
From: Andrew Morton @ 2003-03-07 12:15 UTC (permalink / raw)
To: Jens Axboe; +Cc: tim, linux-kernel
Jens Axboe <axboe@suse.de> wrote:
>
> Hi,
>
> The patch doesn't look right, why is INITIAL_JIFFIES being cast to
> unsigned int? This breaks x86_64 at least.
>
> ...
> -#define INITIAL_JIFFIES ((unsigned int) (-300*HZ))
This sets the initial jiffies value to 0x00000000fffb6c20, which can trigger
32-bit wraparound bugs: if some random jiffy counter wraps from
0x00000000ffffffff to 0x0000000000000000 then things fail.
davem was bitten by at least one such bug in the qlogicfc driver. It would
have caused 64-bit machines to fail after 49 days.
It turns out that it is more valuable to test for this than to test for
64-bit wraparound bugs.
^ permalink raw reply [flat|nested] 3+ messages in thread
* 2.5.64 and jiffies wrap
@ 2003-03-07 13:05 Jens Axboe
2003-03-07 12:15 ` Andrew Morton
0 siblings, 1 reply; 3+ messages in thread
From: Jens Axboe @ 2003-03-07 13:05 UTC (permalink / raw)
To: tim, akpm; +Cc: Linux Kernel
Hi,
The patch doesn't look right, why is INITIAL_JIFFIES being cast to
unsigned int? This breaks x86_64 at least.
--- /opt/kernel/linux-2.5.64/arch/x86_64/kernel/time.c 2003-03-07 13:54:40.000000000 +0100
+++ linux-2.5.64/arch/x86_64/kernel/time.c 2003-03-07 13:17:58.000000000 +0100
@@ -30,7 +30,7 @@
#include <asm/apic.h>
#endif
-u64 jiffies_64;
+u64 jiffies_64 = INITIAL_JIFFIES;
extern int using_apic_timer;
--- /opt/kernel/linux-2.5.64/include/linux/time.h 2003-03-07 13:54:41.000000000 +0100
+++ linux-2.5.64/include/linux/time.h 2003-03-07 13:18:10.000000000 +0100
@@ -31,7 +31,7 @@
* Have the 32 bit jiffies value wrap 5 minutes after boot
* so jiffies wrap bugs show up earlier.
*/
-#define INITIAL_JIFFIES ((unsigned int) (-300*HZ))
+#define INITIAL_JIFFIES ((unsigned long) (-300*HZ))
/*
* Change timeval to jiffies, trying to avoid the
--
Jens Axboe
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: 2.5.64 and jiffies wrap
2003-03-07 12:15 ` Andrew Morton
@ 2003-03-07 13:20 ` Jens Axboe
0 siblings, 0 replies; 3+ messages in thread
From: Jens Axboe @ 2003-03-07 13:20 UTC (permalink / raw)
To: Andrew Morton; +Cc: tim, linux-kernel
On Fri, Mar 07 2003, Andrew Morton wrote:
> Jens Axboe <axboe@suse.de> wrote:
> >
> > Hi,
> >
> > The patch doesn't look right, why is INITIAL_JIFFIES being cast to
> > unsigned int? This breaks x86_64 at least.
> >
> > ...
> > -#define INITIAL_JIFFIES ((unsigned int) (-300*HZ))
>
> This sets the initial jiffies value to 0x00000000fffb6c20, which can trigger
> 32-bit wraparound bugs: if some random jiffy counter wraps from
> 0x00000000ffffffff to 0x0000000000000000 then things fail.
>
> davem was bitten by at least one such bug in the qlogicfc driver. It would
> have caused 64-bit machines to fail after 49 days.
>
> It turns out that it is more valuable to test for this than to test for
> 64-bit wraparound bugs.
Ok makes sense, I thought the point was just to test for jiffies wrap.
Anyways, the patch breaks boot on x86_64 here.
--
Jens Axboe
^ permalink raw reply [flat|nested] 3+ messages in thread
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2003-03-07 13:05 2.5.64 and jiffies wrap Jens Axboe
2003-03-07 12:15 ` Andrew Morton
2003-03-07 13:20 ` Jens Axboe
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