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From: Pavel Begunkov <asml.silence@gmail.com>
To: Nathan Chancellor <natechancellor@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	io-uring@vger.kernel.org, clang-built-linux@googlegroups.com
Subject: Re: [PATCH 2/2] io_uring: optimise io_fail_links()
Date: Thu, 15 Oct 2020 11:11:52 +0100	[thread overview]
Message-ID: <7e293894-823c-5b91-1b55-f5941c82d83e@gmail.com> (raw)
In-Reply-To: <20201015085319.GA3683749@ubuntu-m3-large-x86>

On 15/10/2020 09:53, Nathan Chancellor wrote:
> On Wed, Oct 14, 2020 at 08:44:22PM +0100, Pavel Begunkov wrote:
>> -		io_put_req_deferred(link, 2);
>> +
>> +		/*
>> +		 * It's ok to free under spinlock as they're not linked anymore,
>> +		 * but avoid REQ_F_WORK_INITIALIZED because it may deadlock on
>> +		 * work.fs->lock.
>> +		 */
>> +		if (link->flags | REQ_F_WORK_INITIALIZED)
>> +			io_put_req_deferred(link, 2);
>> +		else
>> +			io_double_put_req(link);
> 
> fs/io_uring.c:1816:19: warning: bitwise or with non-zero value always
> evaluates to true [-Wtautological-bitwise-compare]
>                 if (link->flags | REQ_F_WORK_INITIALIZED)
>                     ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
> 1 warning generated.
> 
> According to the comment, was it intended for that to be a bitwise AND
> then negated to check for the absence of it? If so, wouldn't it be
> clearer to flip the condition so that a negation is not necessary like
> below? I can send a formal patch if my analysis is correct but if not,
> feel free to fix it yourself and add

I have no idea what have happened, but yeah, there should be "&",
though without any additional negation. That's because deferred
version is safer. 

Nathan, thanks for letting know!
Jens, could you please fold in the change below.


diff --git a/fs/io_uring.c b/fs/io_uring.c
index 66c41d53a9d3..2c83c2688ec5 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1813,7 +1813,7 @@ static void __io_fail_links(struct io_kiocb *req)
 		 * but avoid REQ_F_WORK_INITIALIZED because it may deadlock on
 		 * work.fs->lock.
 		 */
-		if (link->flags | REQ_F_WORK_INITIALIZED)
+		if (link->flags & REQ_F_WORK_INITIALIZED)
 			io_put_req_deferred(link, 2);
 		else
 			io_double_put_req(link);


-- 
Pavel Begunkov



  reply	other threads:[~2020-10-15 10:14 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-14 19:44 [PATCH 0/2] post F_COMP_LOCKED optimisations Pavel Begunkov
2020-10-14 19:44 ` [PATCH 1/2] io_uring: optimise COMP_LOCK-less flush_completion Pavel Begunkov
2020-10-14 19:44 ` [PATCH 2/2] io_uring: optimise io_fail_links() Pavel Begunkov
2020-10-15  8:53   ` Nathan Chancellor
2020-10-15 10:11     ` Pavel Begunkov [this message]
2020-10-15 13:09       ` Jens Axboe
2020-10-14 19:53 ` [PATCH 0/2] post F_COMP_LOCKED optimisations Jens Axboe
2020-10-14 20:00   ` Pavel Begunkov
2020-10-14 20:24     ` Jens Axboe

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