Do not access buffers after dropping reference count

We should not access a buffer after dropping it's reference count otherwise we could race with another thread that releases the final reference count and frees the buffer causing us to access potentially unmapped memory.

Lachlan

@@ -839,6 +839,7 @@ xfs_buf_rele(

		return;
	}

+	ASSERT(atomic_read(&bp->b_hold) > 0);
	if (atomic_dec_and_lock(&bp->b_hold, &hash->bh_lock)) {
		if (bp->b_relse) {
			atomic_inc(&bp->b_hold);
@@ -852,11 +853,6 @@ xfs_buf_rele(
			spin_unlock(&hash->bh_lock);
			xfs_buf_free(bp);
		}

- } else {
- /*
- * Catch reference count leaks
- */

-		ASSERT(atomic_read(&bp->b_hold) >= 0);
	}
}

Looks OK. The commit message should point out this is a problem only for DEBUG kernels, though.

Cheers,

Dave.

Dave Chinner
[email protected]

Okay, will do.