dm crypt: avoid accessing uninitialized tasklet

When neither "no_read_workqueue" nor "no_write_workqueue" are enabled,
tasklet_trylock() in crypt_dec_pending() may still return false due to
an uninitialized state, and dm-crypt will unnecessarily do io completion
in io_queue workqueue instead of current context.

Fix this by adding an 'in_tasklet' flag to dm_crypt_io struct and
initialize it to false in crypt_io_init(). Set this flag to true in
kcryptd_queue_crypt() before calling tasklet_schedule(). If set
crypt_dec_pending() will punt io completion to a workqueue.

This also nicely avoids the tasklet_trylock/unlock hack when tasklets
aren't in use.

Fixes: 8e14f610159d ("dm crypt: do not call bio_endio() from the dm-crypt tasklet")
Cc: stable@vger.kernel.org
Reported-by: Hou Tao <houtao1@huawei.com>
Suggested-by: Ignat Korchagin <ignat@cloudflare.com>
Reviewed-by: Ignat Korchagin <ignat@cloudflare.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index faba1be..2764b4e 100644 (file)
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -72,7 +72,9 @@ struct dm_crypt_io {
        struct crypt_config *cc;
        struct bio *base_bio;
        u8 *integrity_metadata;
-       bool integrity_metadata_from_pool;
+       bool integrity_metadata_from_pool:1;
+       bool in_tasklet:1;
+
        struct work_struct work;
        struct tasklet_struct tasklet;
 
@@ -1731,6 +1733,7 @@ static void crypt_io_init(struct dm_crypt_io *io, struct crypt_config *cc,
        io->ctx.r.req = NULL;
        io->integrity_metadata = NULL;
        io->integrity_metadata_from_pool = false;
+       io->in_tasklet = false;
        atomic_set(&io->io_pending, 0);
 }
 
@@ -1777,14 +1780,13 @@ static void crypt_dec_pending(struct dm_crypt_io *io)
         * our tasklet. In this case we need to delay bio_endio()
         * execution to after the tasklet is done and dequeued.
         */
-       if (tasklet_trylock(&io->tasklet)) {
-               tasklet_unlock(&io->tasklet);
-               bio_endio(base_bio);
+       if (io->in_tasklet) {
+               INIT_WORK(&io->work, kcryptd_io_bio_endio);
+               queue_work(cc->io_queue, &io->work);
                return;
        }
 
-       INIT_WORK(&io->work, kcryptd_io_bio_endio);
-       queue_work(cc->io_queue, &io->work);
+       bio_endio(base_bio);
 }
 
 /*
@@ -2233,6 +2235,7 @@ static void kcryptd_queue_crypt(struct dm_crypt_io *io)
                 * it is being executed with irqs disabled.
                 */
                if (in_hardirq() || irqs_disabled()) {
+                       io->in_tasklet = true;
                        tasklet_init(&io->tasklet, kcryptd_crypt_tasklet, (unsigned long)&io->work);
                        tasklet_schedule(&io->tasklet);
                        return;