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shm: 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.

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

Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Reported-by: Jiri Olsa <olsajiri@gmail.com>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: <stable@kernel.org>		[2.6.everything]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Tony Battersby 2009-02-04 15:12:04 -08:00 committed by Linus Torvalds
parent 1f5e31d7e5
commit a68e61e8ff
1 changed files with 4 additions and 0 deletions
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4
ipc/shm.c
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@ -565,11 +565,15 @@ static void shm_get_stat(struct ipc_namespace *ns, unsigned long *rss,
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
}
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