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Commit 6b9aa7ac authored by Wengang Wang's avatar Wengang Wang Committed by Greg Kroah-Hartman
Browse files

fs/ocfs2: fix race in ocfs2_dentry_attach_lock() 

commit be99ca2716972a712cde46092c54dee5e6192bf8 upstream.

ocfs2_dentry_attach_lock() can be executed in parallel threads against the
same dentry.  Make that race safe.  The race is like this:

            thread A                               thread B

(A1) enter ocfs2_dentry_attach_lock,
seeing dentry->d_fsdata is NULL,
and no alias found by
ocfs2_find_local_alias, so kmalloc
a new ocfs2_dentry_lock structure
to local variable "dl", dl1

               .....

                                    (B1) enter ocfs2_dentry_attach_lock,
                                    seeing dentry->d_fsdata is NULL,
                                    and no alias found by
                                    ocfs2_find_local_alias so kmalloc
                                    a new ocfs2_dentry_lock structure
                                    to local variable "dl", dl2.

                                                   ......

(A2) set dentry->d_fsdata with dl1,
call ocfs2_dentry_lock() and increase
dl1->dl_lockres.l_ro_holders to 1 on
success.
              ......

                                    (B2) set dentry->d_fsdata with dl2
                                    call ocfs2_dentry_lock() and increase
				    dl2->dl_lockres.l_ro_holders to 1 on
				    success.

                                                  ......

(A3) call ocfs2_dentry_unlock()
and decrease
dl2->dl_lockres.l_ro_holders to 0
on success.
             ....

                                    (B3) call ocfs2_dentry_unlock(),
                                    decreasing
				    dl2->dl_lockres.l_ro_holders, but
				    see it's zero now, panic

Link: http://lkml.kernel.org/r/20190529174636.22364-1-wen.gang.wang@oracle.com


Signed-off-by: default avatarWengang Wang <wen.gang.wang@oracle.com>
Reported-by: default avatarDaniel Sobe <daniel.sobe@nxp.com>
Tested-by: default avatarDaniel Sobe <daniel.sobe@nxp.com>
Reviewed-by: default avatarChangwei Ge <gechangwei@live.cn>
Reviewed-by: default avatarJoseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Gang He <ghe@suse.com>
Cc: Jun Piao <piaojun@huawei.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 553a1f0d

fs/ocfs2/dcache.c

+12 −0
Original line number Diff line number Diff line
@@ -310,6 +310,18 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry, 


out_attach:

	spin_lock(&dentry_attach_lock);

	if (unlikely(dentry->d_fsdata && !alias)) {

		/* d_fsdata is set by a racing thread which is doing

		 * the same thing as this thread is doing. Leave the racing

		 * thread going ahead and we return here.

		 */

		spin_unlock(&dentry_attach_lock);

		iput(dl->dl_inode);

		ocfs2_lock_res_free(&dl->dl_lockres);

		kfree(dl);

		return 0;

	}



	dentry->d_fsdata = dl;

	dl->dl_count++;

	spin_unlock(&dentry_attach_lock);