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Subject[PATCH v4 06/11] md/raid5-cache: Drop RCU usage of conf->log
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>
---
drivers/md/raid5-cache.c | 16 +++++-----------
1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index ca8fc317da95..b1fc65e113f8 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -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);
--
2.30.2
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