[patch 13/56] shm: fix shmctl(SHM_INFO) lockup with !CONFIG_SHMEM

[Greg KH]

2.6.27-stable review patch.  If anyone has any objections, please let us know.
------------------

From: Tony Battersby <tonyb@xxxxxxxxxxxxxxx>

commit a68e61e8ff2d46327a37b69056998b47745db6fa upstream.

shm_get_stat() assumes that the inode is a "struct shmem_inode_info",
which is incorrect for !CONFIG_SHMEM (see fs/ramfs/inode.c:
ramfs_get_inode() vs.  mm/shmem.c: shmem_get_inode()).

This bad assumption can cause shmctl(SHM_INFO) to lockup when
shm_get_stat() tries to spin_lock(&info->lock).  Users of !CONFIG_SHMEM
may encounter this lockup simply by invoking the 'ipcs' command.

Reported by Jiri Olsa back in February 2008:
http://lkml.org/lkml/2008/2/29/74

Signed-off-by: Tony Battersby <tonyb@xxxxxxxxxxxxxxx>
Cc: Jiri Kosina <jkosina@xxxxxxx>
Reported-by: Jiri Olsa <olsajiri@xxxxxxxxx>
Cc: Hugh Dickins <hugh@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 ipc/shm.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -565,11 +565,15 @@ static void shm_get_stat(struct ipc_name
 			struct hstate *h = hstate_file(shp->shm_file);
 			*rss += pages_per_huge_page(h) * mapping->nrpages;
 		} else {
+#ifdef CONFIG_SHMEM
 			struct shmem_inode_info *info = SHMEM_I(inode);
 			spin_lock(&info->lock);
 			*rss += inode->i_mapping->nrpages;
 			*swp += info->swapped;
 			spin_unlock(&info->lock);
+#else
+			*rss += inode->i_mapping->nrpages;
+#endif
 		}
 
 		total++;

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