linux-kernel - Re: boot panic after oops from sysfs_new

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Message-ID: <4A9CD41C.8060604@kernel.org>
Date:	Tue, 01 Sep 2009 16:58:20 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Meelis Roos <mroos@...ux.ee>
CC:	David Miller <davem@...emloft.net>, sparclinux@...r.kernel.org,
	Linux Kernel list <linux-kernel@...r.kernel.org>
Subject: Re: boot panic after oops from sysfs_new_dirent

Meelis Roos wrote:
>> Ummm.... one more question.  Is cpu0 missing?  Can you please post the
>> output of "cat /proc/cpuinfo"?
> 
> Yes, there's no CPU numbered 0, the numbers come from hardware slots on 
> backplane.

Aha...  Does the following patch fix the problem?

diff --git a/mm/percpu.c b/mm/percpu.c
index 5fe3784..3311c89 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -197,7 +197,12 @@ static unsigned long pcpu_chunk_addr(struct pcpu_chunk *chunk,
 static bool pcpu_chunk_page_occupied(struct pcpu_chunk *chunk,
 				     int page_idx)
 {
-	return *pcpu_chunk_pagep(chunk, 0, page_idx) != NULL;
+	/*
+	 * Any possible cpu id can be used here, so there's no need to
+	 * worry about preemption or cpu hotplug.
+	 */
+	return *pcpu_chunk_pagep(chunk, raw_smp_processor_id(),
+				 page_idx) != NULL;
 }

 /* set the pointer to a chunk in a page struct */
@@ -297,6 +302,14 @@ static struct pcpu_chunk *pcpu_chunk_addr_search(void *addr)
 		return pcpu_first_chunk;
 	}

+	/*
+	 * The address is relative to unit0 which might be unused and
+	 * thus unmapped.  Offset the address to the unit space of the
+	 * current processor before looking it up in the vmalloc
+	 * space.  Note that any possible cpu id can be used here, so
+	 * there's no need to worry about preemption or cpu hotplug.
+	 */
+	addr += raw_smp_processor_id() * pcpu_unit_size;
 	return pcpu_get_page_chunk(vmalloc_to_page(addr));
 }

-- 
tejun
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