raid5-cache: fix a user-after-free bug

r5l_compress_stripe_end_list() can free an io_unit. This breaks the
assumption only reclaimer can free io_unit. We can add a reference count
based io_unit free, but since only reclaim can wait io_unit becoming to
STRIPE_END state, we use a simple global wait queue here.

Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: NeilBrown <neilb@suse.com>

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 41542ebd813bcfa15f7b0a70609f35c910ea096a..496f8e2578cc3af570450e7b568fd8c61c29e395 100644 (file)
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -79,6 +79,7 @@ struct r5l_log {
                                         * dones't wait for specific io_unit
                                         * switching to IO_UNIT_STRIPE_END
                                         * state) */
+       wait_queue_head_t iounit_wait;
 
        struct list_head no_space_stripes; /* pending stripes, log has no space */
        spinlock_t no_space_stripes_lock;
@@ -109,7 +110,6 @@ struct r5l_io_unit {
        struct list_head stripe_list; /* stripes added to the io_unit */
 
        int state;
-       wait_queue_head_t wait_state;
 };
 
 /* r5l_io_unit state */
@@ -162,7 +162,6 @@ static struct r5l_io_unit *r5l_alloc_io_unit(struct r5l_log *log)
        INIT_LIST_HEAD(&io->log_sibling);
        INIT_LIST_HEAD(&io->stripe_list);
        io->state = IO_UNIT_RUNNING;
-       init_waitqueue_head(&io->wait_state);
        return io;
 }
 
@@ -243,8 +242,8 @@ static void __r5l_set_io_unit_state(struct r5l_io_unit *io,
                        r5l_wake_reclaim(log, 0);
 
                r5l_compress_stripe_end_list(log);
+               wake_up(&log->iounit_wait);
        }
-       wake_up(&io->wait_state);
 }
 
 static void r5l_set_io_unit_state(struct r5l_io_unit *io,
@@ -622,10 +621,11 @@ void r5l_flush_stripe_to_raid(struct r5l_log *log)
        submit_bio(WRITE_FLUSH, &log->flush_bio);
 }
 
-static void r5l_kick_io_unit(struct r5l_log *log, struct r5l_io_unit *io)
+static void r5l_kick_io_unit(struct r5l_log *log)
 {
        md_wakeup_thread(log->rdev->mddev->thread);
-       wait_event(io->wait_state, io->state >= IO_UNIT_STRIPE_END);
+       wait_event_lock_irq(log->iounit_wait, !list_empty(&log->stripe_end_ios),
+                           log->io_list_lock);
 }
 
 static void r5l_write_super(struct r5l_log *log, sector_t cp);
@@ -670,12 +670,7 @@ static void r5l_do_reclaim(struct r5l_log *log)
                else if (!list_empty(&log->running_ios))
                        target_list = &log->running_ios;
 
-               io = list_first_entry(target_list,
-                                     struct r5l_io_unit, log_sibling);
-               spin_unlock_irq(&log->io_list_lock);
-               /* nobody else can delete the io, we are safe */
-               r5l_kick_io_unit(log, io);
-               spin_lock_irq(&log->io_list_lock);
+               r5l_kick_io_unit(log);
        }
        spin_unlock_irq(&log->io_list_lock);
 
@@ -1079,6 +1074,7 @@ int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
                                                 log->rdev->mddev, "reclaim");
        if (!log->reclaim_thread)
                goto reclaim_thread;
+       init_waitqueue_head(&log->iounit_wait);
 
        INIT_LIST_HEAD(&log->no_space_stripes);
        spin_lock_init(&log->no_space_stripes_lock);