Commit c6e8c6cc authored by KaiGai Kohei's avatar KaiGai Kohei Committed by David Woodhouse
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[JFFS2][XATTR] Fix xd->refcnt race condition 



When xd->refcnt is checked whether this xdatum should be released
or not, atomic_dec_and_lock() is used to ensure holding the
c->erase_completion_lock.

This fix change a specification of delete_xattr_datum().
Previously, it's only called when xd->refcnt equals zero.
(calling it with positive xd->refcnt cause a BUG())
If you applied this patch, the function checks whether
xd->refcnt is zero or not under the spinlock if necessary.
Then, it marks xd DEAD flahs and links with xattr_dead_list
or releases it immediately when xd->refcnt become zero.

Signed-off-by: default avatarKaiGai Kohei <kaigai@ak.jp.nec.com>
Signed-off-by: default avatarDavid Woodhouse <dwmw2@infradead.org>
parent ea9b6dcc

fs/jffs2/xattr.c

+22 −23
Original line number Diff line number Diff line
@@ -50,9 +50,10 @@ 
 *   is used to write xdatum to medium. xd->version will be incremented.

 * create_xattr_datum(c, xprefix, xname, xvalue, xsize)

 *   is used to create new xdatum and write to medium.

 * delete_xattr_datum(c, xd)

 *   is used to delete a xdatum. It marks xd JFFS2_XFLAGS_DEAD, and allows

 *   GC to reclaim those physical nodes.

 * unrefer_xattr_datum(c, xd)

 *   is used to delete a xdatum. When nobody refers this xdatum, JFFS2_XFLAGS_DEAD

 *   is set on xd->flags and chained xattr_dead_list or release it immediately.

 *   In the first case, the garbage collector release it later.

 * -------------------------------------------------- */

static uint32_t xattr_datum_hashkey(int xprefix, const char *xname, const char *xvalue, int xsize)

{
@@ -394,14 +395,14 @@ static struct jffs2_xattr_datum *create_xattr_datum(struct jffs2_sb_info *c, 
	return xd;

}



static void delete_xattr_datum(struct jffs2_sb_info *c, struct jffs2_xattr_datum *xd)

static void unrefer_xattr_datum(struct jffs2_sb_info *c, struct jffs2_xattr_datum *xd)

{

	/* must be called under down_write(xattr_sem) */

	BUG_ON(atomic_read(&xd->refcnt));

	if (atomic_dec_and_lock(&xd->refcnt, &c->erase_completion_lock)) {

		uint32_t xid = xd->xid, version = xd->version;



		unload_xattr_datum(c, xd);

		xd->flags |= JFFS2_XFLAGS_DEAD;

	spin_lock(&c->erase_completion_lock);

		if (xd->node == (void *)xd) {

			BUG_ON(!(xd->flags & JFFS2_XFLAGS_INVALID));

			jffs2_free_xattr_datum(xd);
@@ -409,7 +410,9 @@ static void delete_xattr_datum(struct jffs2_sb_info *c, struct jffs2_xattr_datum 
			list_add(&xd->xindex, &c->xattr_dead_list);

		}

		spin_unlock(&c->erase_completion_lock);

	dbg_xattr("xdatum(xid=%u, version=%u) was removed.\n", xd->xid, xd->version);



		dbg_xattr("xdatum(xid=%u, version=%u) was removed.\n", xid, version);

	}

}



/* -------- xref related functions ------------------
@@ -580,8 +583,7 @@ static void delete_xattr_ref(struct jffs2_sb_info *c, struct jffs2_xattr_ref *re 
	dbg_xattr("xref(ino=%u, xid=%u, xseqno=%u) was removed.\n",

		  ref->ino, ref->xid, ref->xseqno);



	if (atomic_dec_and_test(&xd->refcnt))

		delete_xattr_datum(c, xd);

	unrefer_xattr_datum(c, xd);

}



void jffs2_xattr_delete_inode(struct jffs2_sb_info *c, struct jffs2_inode_cache *ic)
@@ -1119,8 +1121,7 @@ int do_jffs2_setxattr(struct inode *inode, int xprefix, const char *xname, 
					ref->next = c->xref_dead_list;

					c->xref_dead_list = ref;

					spin_unlock(&c->erase_completion_lock);

					if (atomic_dec_and_test(&xd->refcnt))

						delete_xattr_datum(c, xd);

					unrefer_xattr_datum(c, xd);

				} else {

					ref->ic = ic;

					ref->xd = xd;
@@ -1156,8 +1157,7 @@ int do_jffs2_setxattr(struct inode *inode, int xprefix, const char *xname, 
	down_write(&c->xattr_sem);

	if (rc) {

		JFFS2_WARNING("jffs2_reserve_space()=%d, request=%u\n", rc, request);

		if (atomic_dec_and_test(&xd->refcnt))

			delete_xattr_datum(c, xd);

		unrefer_xattr_datum(c, xd);

		up_write(&c->xattr_sem);

		return rc;

	}
@@ -1170,8 +1170,7 @@ int do_jffs2_setxattr(struct inode *inode, int xprefix, const char *xname, 
			ic->xref = ref;

		}

		rc = PTR_ERR(newref);

		if (atomic_dec_and_test(&xd->refcnt))

			delete_xattr_datum(c, xd);

		unrefer_xattr_datum(c, xd);

	} else if (ref) {

		delete_xattr_ref(c, ref);

	}

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