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author | Lars Ellenberg <lars.ellenberg@linbit.com> | 2011-10-06 15:10:34 (GMT) |
---|---|---|
committer | Philipp Reisner <philipp.reisner@linbit.com> | 2012-05-09 13:15:52 (GMT) |
commit | 6a9a92f4ef05bb3e94bbfe123c21482fa5da9866 (patch) | |
tree | f7eb75744c834b287d1656b6763cb5bb7a1402ef /drivers/block/drbd | |
parent | 5ba3dac52126699e541ac3ee37aad890ca835fc1 (diff) | |
download | linux-fsl-qoriq-6a9a92f4ef05bb3e94bbfe123c21482fa5da9866.tar.xz |
drbd: fix harmless race to not trigger an ASSERT
We have one pre-allocated page to do certain synchronous meta data IO with,
using it is serialized like so:
drbd_md_get_buffer();
drbd_md_sync_page_io();
drbd_md_sync_page_io();
...
drbd_md_put_buffer();
In drbd_md_sync_page_io() there is an
ASSERT(atomic_read(&mdev->md_io_in_use) == 1);
We want to be able to timeout on unresponsive lower level devices, so we
can "detach" in that case. Inside drbd_md_sync_page_io() we grab an extra
reference, to not have a dangling pointer in case a delayed IO eventually
does still complete, even after we "detached" already.
We need to put the extra reference before we signal completion from the
completion handler, or the second drbd_md_sync_page_io() above may
trigger the assert (reference count still 2).
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Diffstat (limited to 'drivers/block/drbd')
-rw-r--r-- | drivers/block/drbd/drbd_worker.c | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/drivers/block/drbd/drbd_worker.c b/drivers/block/drbd/drbd_worker.c index 933091f..62bde5a 100644 --- a/drivers/block/drbd/drbd_worker.c +++ b/drivers/block/drbd/drbd_worker.c @@ -77,10 +77,21 @@ void drbd_md_io_complete(struct bio *bio, int error) md_io->error = error; + /* We grabbed an extra reference in _drbd_md_sync_page_io() to be able + * to timeout on the lower level device, and eventually detach from it. + * If this io completion runs after that timeout expired, this + * drbd_md_put_buffer() may allow us to finally try and re-attach. + * During normal operation, this only puts that extra reference + * down to 1 again. + * Make sure we first drop the reference, and only then signal + * completion, or we may (in drbd_al_read_log()) cycle so fast into the + * next drbd_md_sync_page_io(), that we trigger the + * ASSERT(atomic_read(&mdev->md_io_in_use) == 1) there. + */ + drbd_md_put_buffer(mdev); md_io->done = 1; wake_up(&mdev->misc_wait); bio_put(bio); - drbd_md_put_buffer(mdev); put_ldev(mdev); } |