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gfs2: fix an oops in gfs2_permission

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[ Upstream commit 0abd1557e21c617bd13fc18f7725fc6363c05913 ]

In RCU mode, we might race with gfs2_evict_inode(), which zeroes
->i_gl.  Freeing of the object it points to is RCU-delayed, so
if we manage to fetch the pointer before it's been replaced with
NULL, we are fine.  Check if we'd fetched NULL and treat that
as "bail out and tell the caller to get out of RCU mode".

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Al Viro 2023-10-02 03:33:44 +01:00 committed by Greg Kroah-Hartman
parent 2a054b87a1
commit 5f8d51a04b
2 changed files with 10 additions and 3 deletions
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11
fs/gfs2/inode.c
View File

@ -1837,14 +1837,21 @@ int gfs2_permission(struct inode *inode, int mask)
{
struct gfs2_inode *ip;
struct gfs2_holder i_gh;
struct gfs2_glock *gl;
int error;
gfs2_holder_mark_uninitialized(&i_gh);
ip = GFS2_I(inode);
if (gfs2_glock_is_locked_by_me(ip->i_gl) == NULL) {
gl = rcu_dereference(ip->i_gl);
if (unlikely(!gl)) {
/* inode is getting torn down, must be RCU mode */
WARN_ON_ONCE(!(mask & MAY_NOT_BLOCK));
return -ECHILD;
}
if (gfs2_glock_is_locked_by_me(gl) == NULL) {
if (mask & MAY_NOT_BLOCK)
return -ECHILD;
error = gfs2_glock_nq_init(ip->i_gl, LM_ST_SHARED, LM_FLAG_ANY, &i_gh);
error = gfs2_glock_nq_init(gl, LM_ST_SHARED, LM_FLAG_ANY, &i_gh);
if (error)
return error;
}

2
fs/gfs2/super.c
View File

@ -1471,7 +1471,7 @@ static void gfs2_evict_inode(struct inode *inode)
wait_on_bit_io(&ip->i_flags, GIF_GLOP_PENDING, TASK_UNINTERRUPTIBLE);
gfs2_glock_add_to_lru(ip->i_gl);
gfs2_glock_put_eventually(ip->i_gl);
ip->i_gl = NULL;
rcu_assign_pointer(ip->i_gl, NULL);
}
}