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md/raid5-cache: Drop RCU usage of conf->log

Browse source 
The only place that uses RCU to access conf->log is in
r5l_log_disk_error(). This function is mostly used in the IO path
and once with mddev_lock() held in raid5_change_consistency_policy().

It is known that the IO will be suspended before the log is freed and
r5l_log_exit() is called with the mddev_lock() held.

This should mean that conf->log can not be freed while the function is
being called, so the RCU protection is not necessary. Drop the
rcu_read_lock() as well as the synchronize_rcu() and
rcu_assign_pointer() usage.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Song Liu <song@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Logan Gunthorpe 2022-06-08 10:27:51 -06:00 • committed by Jens Axboe
parent 78ede6a06f
commit 7769085c8d
1 changed files with 5 additions and 11 deletions
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16
drivers/md/raid5-cache.c
View file

@ -1590,18 +1590,13 @@ void r5l_quiesce(struct r5l_log *log, int quiesce)
bool r5l_log_disk_error(struct r5conf *conf)
{
struct r5l_log *log;
bool ret;
/* don't allow write if journal disk is missing */
rcu_read_lock();
log = rcu_dereference(conf->log);
struct r5l_log *log = conf->log;
/* don't allow write if journal disk is missing */
if (!log)
ret = test_bit(MD_HAS_JOURNAL, &conf->mddev->flags);
return test_bit(MD_HAS_JOURNAL, &conf->mddev->flags);
else
ret = test_bit(Faulty, &log->rdev->flags);
rcu_read_unlock();
return ret;
return test_bit(Faulty, &log->rdev->flags);
}
#define R5L_RECOVERY_PAGE_POOL_SIZE 256
@ -3148,7 +3143,7 @@ int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
spin_lock_init(&log->stripe_in_journal_lock);
atomic_set(&log->stripe_in_journal_count, 0);
rcu_assign_pointer(conf->log, log);
conf->log = log;
set_bit(MD_HAS_JOURNAL, &conf->mddev->flags);
return 0;
@ -3171,7 +3166,6 @@ void r5l_exit_log(struct r5conf *conf)
struct r5l_log *log = conf->log;
conf->log = NULL;
synchronize_rcu();
/* Ensure disable_writeback_work wakes up and exits */
wake_up(&conf->mddev->sb_wait);