[PATCH v2 11/17] md/raid5: Ensure array is suspended for calls to log_exit()

Logan Gunthorpe
2022-05-26T16:37:49Z

The raid5-cache code relies on there being no IO in flight when
log_exit() is called. There are two places where this is not
guaranteed so add mddev_suspend() and mddev_resume() calls to these
sites.

The site in raid5_remove_disk() has a comment saying that it is
called in raid5d and thus cannot wait for pending writes; however that
does not appear to be correct anymore (if it ever was) as
raid5_remove_disk() is called from hot_remove_disk() which only
appears to be called in the md_ioctl(). Thus, the comment is removed,
as well as the racy check and replaced with calls to suspend/resume.

The site in raid5_change_consistency_policy() is in the error path,
and another similar call site already has suspend/resume calls just
below it; so it should be equally safe to make that change here.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
drivers/md/raid5.c | 18 ++++++------------
1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 0d486f8aaf87..4b25a0262cb5 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -7938,18 +7938,9 @@ static int raid5_remove_disk(struct mddev *mddev, struct md_rdev *rdev)

print_raid5_conf(conf);
if (test_bit(Journal, &rdev->flags) && conf->log) {
- /*
- * we can't wait pending write here, as this is called in
- * raid5d, wait will deadlock.
- * neilb: there is no locking about new writes here,
- * so this cannot be safe.
- */
- if (atomic_read(&conf->active_stripes) ||
- atomic_read(&conf->r5c_cached_full_stripes) ||
- atomic_read(&conf->r5c_cached_partial_stripes)) {
- return -EBUSY;
- }
+ mddev_suspend(mddev);
log_exit(conf);
+ mddev_resume(mddev);
return 0;
}
if (rdev == rcu_access_pointer(p->rdev))
@@ -8697,8 +8688,11 @@ static int raid5_change_consistency_policy(struct mddev *mddev, const char *buf)
err = log_init(conf, NULL, true);
if (!err) {
err = resize_stripes(conf, conf->pool_size);
- if (err)
+ if (err) {
+ mddev_suspend(mddev);
log_exit(conf);
+ mddev_resume(mddev);
+ }
}
} else
err = -EINVAL;
--
2.30.2