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Re: Kernel 2.6.19.2 New RAID 5 Bug (oops when writing Samba -> RAID5)

To: Justin Piszcz <jpiszcz@xxxxxxxxxxxxxxx>
Subject: Re: Kernel 2.6.19.2 New RAID 5 Bug (oops when writing Samba -> RAID5)
From: Andrew Morton <akpm@xxxxxxxx>
Date: Fri, 26 Jan 2007 01:25:05 -0800
Cc: Chuck Ebbert <cebbert@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, linux-raid@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, Neil Brown <neilb@xxxxxxx>
In-reply-to: <Pine.LNX.4.64.0701241836590.2930@xxxxxxxxxxxxxxxx>
References: <Pine.LNX.4.64.0701200718290.29223@xxxxxxxxxxxxxxxx> <45B5261B.1050104@xxxxxxxxxx> <Pine.LNX.4.64.0701241836590.2930@xxxxxxxxxxxxxxxx>
Sender: xfs-bounce@xxxxxxxxxxx
On Wed, 24 Jan 2007 18:37:15 -0500 (EST)
Justin Piszcz <jpiszcz@xxxxxxxxxxxxxxx> wrote:

> > Without digging too deeply, I'd say you've hit the same bug Sami Farin and
> > others
> > have reported starting with 2.6.19: pages mapped with kmap_atomic() become
> > unmapped
> > during memcpy() or similar operations.  Try disabling preempt -- that seems 
> > to
> > be the
> > common factor.
> > 
> > 
> > -
> > To unsubscribe from this list: send the line "unsubscribe linux-raid" in
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> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > 
> > 
> 
> After I run some other tests, I am going to re-run this test and see if it 
> OOPSes again with PREEMPT off.

Strange.  The below debug patch might catch it - please run with this
applied.  


--- a/arch/i386/mm/highmem.c~kmap_atomic-debugging
+++ a/arch/i386/mm/highmem.c
@@ -30,7 +30,43 @@ void *kmap_atomic(struct page *page, enu
 {
        enum fixed_addresses idx;
        unsigned long vaddr;
+       static unsigned warn_count = 10;
 
+       if (unlikely(warn_count == 0))
+               goto skip;
+
+       if (unlikely(in_interrupt())) {
+               if (in_irq()) {
+                       if (type != KM_IRQ0 && type != KM_IRQ1 &&
+                           type != KM_BIO_SRC_IRQ && type != KM_BIO_DST_IRQ &&
+                           type != KM_BOUNCE_READ) {
+                               WARN_ON(1);
+                               warn_count--;
+                       }
+               } else if (!irqs_disabled()) {  /* softirq */
+                       if (type != KM_IRQ0 && type != KM_IRQ1 &&
+                           type != KM_SOFTIRQ0 && type != KM_SOFTIRQ1 &&
+                           type != KM_SKB_SUNRPC_DATA &&
+                           type != KM_SKB_DATA_SOFTIRQ &&
+                           type != KM_BOUNCE_READ) {
+                               WARN_ON(1);
+                               warn_count--;
+                       }
+               }
+       }
+
+       if (type == KM_IRQ0 || type == KM_IRQ1 || type == KM_BOUNCE_READ) {
+               if (!irqs_disabled()) {
+                       WARN_ON(1);
+                       warn_count--;
+               }
+       } else if (type == KM_SOFTIRQ0 || type == KM_SOFTIRQ1) {
+               if (irq_count() == 0 && !irqs_disabled()) {
+                       WARN_ON(1);
+                       warn_count--;
+               }
+       }
+skip:
        /* even !CONFIG_PREEMPT needs this, for in_atomic in do_page_fault */
        pagefault_disable();
        if (!PageHighMem(page))
_


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