From: Nick Piggin <npiggin@suse.de>
Date: Tue, 10 Oct 2006 02:36:54 +0000 (+0200)
Subject: [PATCH] mm: bug in set_page_dirty_buffers
X-Git-Tag: v2.6.19-rc2~206
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ebf7a227dd1d810203a19642655d2fa293f395dd;p=linux-2.6

[PATCH] mm: bug in set_page_dirty_buffers

This was triggered, but not the fault of, the dirty page accounting
patches. Suitable for -stable as well, after it goes upstream.

  Unable to handle kernel NULL pointer dereference at virtual address 0000004c
  EIP is at _spin_lock+0x12/0x66
  Call Trace:
   [<401766e7>] __set_page_dirty_buffers+0x15/0xc0
   [<401401e7>] set_page_dirty+0x2c/0x51
   [<40140db2>] set_page_dirty_balance+0xb/0x3b
   [<40145d29>] __do_fault+0x1d8/0x279
   [<40147059>] __handle_mm_fault+0x125/0x951
   [<401133f1>] do_page_fault+0x440/0x59f
   [<4034d0c1>] error_code+0x39/0x40
   [<08048a33>] 0x8048a33

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---

diff --git a/fs/buffer.c b/fs/buffer.c
index 16cfbcd254..eeb8ac1aa8 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -701,7 +701,10 @@ EXPORT_SYMBOL(mark_buffer_dirty_inode);
  */
 int __set_page_dirty_buffers(struct page *page)
 {
-	struct address_space * const mapping = page->mapping;
+	struct address_space * const mapping = page_mapping(page);
+
+	if (unlikely(!mapping))
+		return !TestSetPageDirty(page);
 
 	spin_lock(&mapping->private_lock);
 	if (page_has_buffers(page)) {