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GFS2: Fix race in gfs2_rs_alloc 

QE aio tests uncovered a race condition in gfs2_rs_alloc where it's possible
to come out of the function with a valid ip->i_res allocation but it gets
freed before use resulting in a NULL ptr dereference.

This patch envelopes the initial short-circuit check for non-NULL ip->i_res
into the mutex lock. With this patch, I was able to successfully run the
reproducer test multiple times.

Resolves: rhbz#878476
Signed-off-by: Abhi Das <adas@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
This commit is contained in:
Abhijith Das 2012-12-19 10:48:01 -05:00 committed by Steven Whitehouse
parent ec1487528b
commit f1213cacc7
1 changed files with 11 additions and 13 deletions
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24
fs/gfs2/rgrp.c
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@ -557,22 +557,20 @@ void gfs2_free_clones(struct gfs2_rgrpd *rgd)
*/
int gfs2_rs_alloc(struct gfs2_inode *ip)
{
struct gfs2_blkreserv *res;
if (ip->i_res)
return 0;
res = kmem_cache_zalloc(gfs2_rsrv_cachep, GFP_NOFS);
if (!res)
return -ENOMEM;
RB_CLEAR_NODE(&res->rs_node);
int error = 0;
down_write(&ip->i_rw_mutex);
if (ip->i_res)
kmem_cache_free(gfs2_rsrv_cachep, res);
else
ip->i_res = res;
goto out;
ip->i_res = kmem_cache_zalloc(gfs2_rsrv_cachep, GFP_NOFS);
if (!ip->i_res) {
error = -ENOMEM;
goto out;
}
RB_CLEAR_NODE(&ip->i_res->rs_node);
out:
up_write(&ip->i_rw_mutex);
return 0;
}