linux-kernel - [PATCH 1/2] fix shmctl(SHM_INFO) lockup with !CONFIG

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Date:	Tue, 27 Jan 2009 17:47:04 -0500
From:	Tony Battersby <tonyb@...ernetics.com>
To:	linux-kernel@...r.kernel.org
Cc:	Jiri Olsa <olsajiri@...il.com>, Jiri Kosina <jkosina@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 1/2] fix shmctl(SHM_INFO) lockup with !CONFIG_SHMEM

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.

Signed-off-by: Tony Battersby <tonyb@...ernetics.com>
CC: <stable@...nel.org>
---

This bug was reported by Jiri Olsa back in February 2008; CC'ing the
people involved in the original discussion.
http://lkml.org/lkml/2008/2/29/74

--- linux-2.6.29-rc2-git3/ipc/shm.c.orig	2009-01-27 16:23:10.000000000 -0500
+++ linux-2.6.29-rc2-git3/ipc/shm.c	2009-01-27 16:23:32.000000000 -0500
@@ -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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