From: Ming Lei <ming.lei@redhat.com>
To: Bart Van Assche <bvanassche@acm.org>
Cc: linux-nvme@lists.infradead.org, linux-scsi@vger.kernel.org,
Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org,
"Martin K . Petersen" <martin.petersen@oracle.com>,
Christoph Hellwig <hch@lst.de>,
Khazhy Kumykov <khazhy@google.com>,
Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>,
Hannes Reinecke <hare@suse.de>,
John Garry <john.garry@huawei.com>,
David Jeffery <djeffery@redhat.com>
Subject: Re: [PATCH 8/8] blk-mq: clear stale request in tags->rq[] before freeing one request pool
Date: Mon, 26 Apr 2021 10:07:03 +0800 [thread overview]
Message-ID: <YIYgR65kR79ghol4@T590> (raw)
In-Reply-To: <69764ff2-f339-0dc0-aac0-a1f9f4b30d53@acm.org>
On Sun, Apr 25, 2021 at 06:50:48PM -0700, Bart Van Assche wrote:
> On 4/25/21 5:49 PM, Ming Lei wrote:
> > On Sun, Apr 25, 2021 at 01:42:59PM -0700, Bart Van Assche wrote:
> >> Using cmpxchg() on set->tags[] is only safe if all other set->tags[]
> >> accesses are changed into WRITE_ONCE() or READ_ONCE().
> >
> > Why?
> >
> > Semantic of cmpxchg() is to modify value pointed by the address if its
> > old value is same with passed 'rq'. That is exactly what we need.
> >
> > writting 'void *' is always atomic. if someone has touched
> > '->rqs[tag]', cmpxchg() won't modify the value.
>
> WRITE_ONCE() supports data types that have the same size as char, short,
> int, long and long long. That includes void *. If writes to these data
> types would always be atomic then we wouldn't need the WRITE_ONCE()
> macro.
OK, then we don't need WRITE_ONCE(), since WRITE on tags->rqs[i] is
always atomic.
Thanks,
Ming
next prev parent reply other threads:[~2021-04-26 2:07 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-25 8:57 [PATCH 0/8] blk-mq: fix request UAF related with iterating over tagset requests Ming Lei
2021-04-25 8:57 ` [PATCH 1/8] Revert "blk-mq: Fix races between blk_mq_update_nr_hw_queues() and iterating over tags" Ming Lei
2021-04-25 8:57 ` [PATCH 2/8] Revert "blk-mq: Make it safe to use RCU to iterate over blk_mq_tag_set.tag_list" Ming Lei
2021-04-25 8:57 ` [PATCH 3/8] Revert "blk-mq: Fix races between iterating over requests and freeing requests" Ming Lei
2021-04-25 8:57 ` [PATCH 4/8] Revert "blk-mq: Introduce atomic variants of blk_mq_(all_tag|tagset_busy)_iter" Ming Lei
2021-04-25 8:57 ` [PATCH 5/8] blk-mq: blk_mq_complete_request_locally Ming Lei
2021-04-25 8:57 ` [PATCH 6/8] block: drivers: complete request locally from blk_mq_tagset_busy_iter Ming Lei
2021-04-26 3:02 ` Bart Van Assche
2021-04-26 6:24 ` Ming Lei
2021-04-27 8:54 ` Ming Lei
2021-04-25 8:57 ` [PATCH 7/8] blk-mq: grab rq->refcount before calling ->fn in blk_mq_tagset_busy_iter Ming Lei
2021-04-25 18:55 ` Bart Van Assche
2021-04-26 0:41 ` Ming Lei
2021-04-25 8:57 ` [PATCH 8/8] blk-mq: clear stale request in tags->rq[] before freeing one request pool Ming Lei
2021-04-25 20:42 ` Bart Van Assche
2021-04-26 0:49 ` Ming Lei
2021-04-26 1:50 ` Bart Van Assche
2021-04-26 2:07 ` Ming Lei [this message]
2021-04-25 9:27 ` [PATCH 0/8] blk-mq: fix request UAF related with iterating over tagset requests Ming Lei
2021-04-25 20:53 ` Bart Van Assche
2021-04-26 1:19 ` Ming Lei
2021-04-26 1:57 ` Bart Van Assche
2021-04-25 16:17 ` Jens Axboe
2021-04-25 18:39 ` Bart Van Assche
2021-04-25 20:18 ` Jens Axboe
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