From: Tejun Heo <tj@kernel.org>
To: torvalds@linux-foundation.org, jannh@google.com,
paulmck@linux.vnet.ibm.com, bcrl@kvack.org,
viro@zeniv.linux.org.uk, kent.overstreet@gmail.com
Cc: security@kernel.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com, Tejun Heo <tj@kernel.org>,
Bart Van Assche <bart.vanassche@wdc.com>,
Jens Axboe <axboe@kernel.dk>
Subject: [PATCH 5/7] block: Remove superflous rcu_read_[un]lock_sched() in blk_queue_enter()
Date: Tue, 6 Mar 2018 09:33:14 -0800 [thread overview]
Message-ID: <20180306173316.3088458-5-tj@kernel.org> (raw)
In-Reply-To: <20180306173316.3088458-1-tj@kernel.org>
3a0a529971ec ("block, scsi: Make SCSI quiesce and resume work
reliably") added rcu_read_[un]lock_sched() to blk_queue_enter() along
with other changes but it doesn't seem to be doing anything.
blk_queue_enter() is called with @q - the pointer to the target
request_queue, so the caller obviously has to guarantee that @q can be
dereferenced, and inside the RCU-sched protected area, there's nothing
which needs further protection.
Let's remove the superflous rcu_read_[un]lock_sched().
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
---
Hello, Bart.
This came up while auditing percpu_ref users for problematic RCU
usages. I couldn't understand what the RCU protection was doing.
It'd be great if you can take a look and tell me whether I missed
something.
Thanks.
block/blk-core.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index 6d82c4f..e3b4d1849 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -827,7 +827,6 @@ int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)
bool success = false;
int ret;
- rcu_read_lock_sched();
if (percpu_ref_tryget_live(&q->q_usage_counter)) {
/*
* The code that sets the PREEMPT_ONLY flag is
@@ -840,7 +839,6 @@ int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)
percpu_ref_put(&q->q_usage_counter);
}
}
- rcu_read_unlock_sched();
if (success)
return 0;
--
2.9.5
next prev parent reply other threads:[~2018-03-06 17:33 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-06 17:26 [PATCHSET] percpu_ref, RCU: Audit RCU usages in percpu_ref users Tejun Heo
2018-03-06 17:33 ` [PATCH 1/7] fs/aio: Add explicit RCU grace period when freeing kioctx Tejun Heo
2018-03-06 17:33 ` [PATCH 2/7] fs/aio: Use RCU accessors for kioctx_table->table[] Tejun Heo
2018-03-06 17:33 ` [PATCH 3/7] RDMAVT: Fix synchronization around percpu_ref Tejun Heo
2018-03-07 15:39 ` Dennis Dalessandro
2018-03-06 17:33 ` [PATCH 4/7] HMM: Remove superflous RCU protection around radix tree lookup Tejun Heo
2018-03-06 17:59 ` Jerome Glisse
2018-03-06 17:33 ` Tejun Heo [this message]
2018-03-06 17:52 ` [PATCH 5/7] block: Remove superflous rcu_read_[un]lock_sched() in blk_queue_enter() Bart Van Assche
2018-03-14 18:46 ` tj
2018-03-14 20:05 ` Bart Van Assche
2018-03-14 20:08 ` Peter Zijlstra
2018-03-14 20:14 ` Bart Van Assche
2018-03-06 17:33 ` [PATCH 6/7] percpu_ref: Update doc to dissuade users from depending on internal RCU grace periods Tejun Heo
2018-03-06 17:33 ` [PATCH 7/7] RCU, workqueue: Implement rcu_work Tejun Heo
2018-03-06 18:30 ` Linus Torvalds
2018-03-09 15:37 ` Tejun Heo
2018-03-07 2:49 ` Lai Jiangshan
2018-03-07 14:54 ` Paul E. McKenney
2018-03-07 16:23 ` Peter Zijlstra
2018-03-07 17:58 ` Paul E. McKenney
2018-03-08 0:29 ` Lai Jiangshan
2018-03-08 17:28 ` Paul E. McKenney
2018-03-09 16:21 ` Tejun Heo
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