linux-kernel - [PATCH] tmpfs: fix highmem swapoff crash regression

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Date:	Fri, 20 May 2011 15:47:33 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Witold Baryluk <baryluk@....if.uj.edu.pl>,
	Nitin Gupta <ngupta@...are.org>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH] tmpfs: fix highmem swapoff crash regression

Commit 778dd893ae78 "tmpfs: fix race between umount and swapoff"
forgot the new rules for strict atomic kmap nesting, causing
WARNING: at arch/x86/mm/highmem_32.c:81 from __kunmap_atomic(), then
BUG: unable to handle kernel paging request at fffb9000 from shmem_swp_set()
when shmem_unuse_inode() is handling swapoff with highmem in use.
My disgrace again.  See https://bugzilla.kernel.org/show_bug.cgi?id=35352

Reported-by: Witold Baryluk <baryluk@....if.uj.edu.pl>
Signed-off-by: Hugh Dickins <hughd@...gle.com>
Cc: stable@...nel.org
---

 mm/shmem.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- 2.6.39/mm/shmem.c	2011-05-18 21:06:34.000000000 -0700
+++ linux/mm/shmem.c	2011-05-20 13:57:20.778870967 -0700
@@ -916,11 +916,12 @@ static int shmem_unuse_inode(struct shme
 			if (size > ENTRIES_PER_PAGE)
 				size = ENTRIES_PER_PAGE;
 			offset = shmem_find_swp(entry, ptr, ptr+size);
+			shmem_swp_unmap(ptr);
 			if (offset >= 0) {
 				shmem_dir_unmap(dir);
+				ptr = shmem_swp_map(subdir);
 				goto found;
 			}
-			shmem_swp_unmap(ptr);
 		}
 	}
 lost1:
--
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