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To:     kernel test robot <lkp@intel.com>
Cc:     kbuild-all@lists.01.org, clang-built-linux@googlegroups.com,
        linux-kernel@vger.kernel.org, Jens Axboe <axboe@kernel.dk>
References: <202103231939.qtWh2L33-lkp@intel.com>
From:   Pavel Begunkov <asml.silence@gmail.com>
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Subject: Re: fs/io_uring.c:6920:12: warning: stack frame size of 1040 bytes in
 function 'io_submit_sqes'
Message-ID: <a8a053dd-5ba1-5c03-8915-f84c7938adf9@gmail.com>
Date:   Tue, 23 Mar 2021 12:51:16 +0000
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In-Reply-To: <202103231939.qtWh2L33-lkp@intel.com>
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On 23/03/2021 11:31, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   84196390620ac0e5070ae36af84c137c6216a7dc
> commit: e5d1bc0a91f16959aa279aa3ee9fdc246d4bb382 io_uring: defer flushing cached reqs
> date:   6 weeks ago
> config: powerpc64-randconfig-r023-20210323 (attached as .config)
> compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 14696baaf4c43fe53f738bc292bbe169eed93d5d)
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # install powerpc64 cross compiling tool for clang build
>         # apt-get install binutils-powerpc64-linux-gnu
>         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e5d1bc0a91f16959aa279aa3ee9fdc246d4bb382
>         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>         git fetch --no-tags linus master
>         git checkout e5d1bc0a91f16959aa279aa3ee9fdc246d4bb382
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=powerpc64 
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
> 
> All warnings (new ones prefixed by >>):
> 
>>> fs/io_uring.c:6920:12: warning: stack frame size of 1040 bytes in function 'io_submit_sqes' [-Wframe-larger-than=]
>    static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr)
>               ^
>    1 warning generated. b

I don't know, for up-to-date code all submission functions are under
128 bytes for me, including io_submit_sqes with everything heavily
inlined into it. I believe it's just a strange config keeping
everything on stack for some reason (too under optimised?).


> 
> 
> vim +/io_submit_sqes +6920 fs/io_uring.c
> 
> 0553b8bda8709c Pavel Begunkov 2020-04-08  6919  
> 0f2122045b9462 Jens Axboe     2020-09-13 @6920  static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr)
> 6c271ce2f1d572 Jens Axboe     2019-01-10  6921  {
> 863e05604a6fb4 Pavel Begunkov 2020-10-27  6922  	struct io_submit_link link;
> 9e645e1105ca60 Jens Axboe     2019-05-10  6923  	int i, submitted = 0;
> 6c271ce2f1d572 Jens Axboe     2019-01-10  6924  
> c4a2ed72c9a615 Jens Axboe     2019-11-21  6925  	/* if we have a backlog and couldn't flush it all, return BUSY */
> ad3eb2c89fb24d Jens Axboe     2019-12-18  6926  	if (test_bit(0, &ctx->sq_check_overflow)) {
> 6c503150ae33ee Pavel Begunkov 2021-01-04  6927  		if (!__io_cqring_overflow_flush(ctx, false, NULL, NULL))
> 1d7bb1d50fb4dc Jens Axboe     2019-11-06  6928  			return -EBUSY;
> ad3eb2c89fb24d Jens Axboe     2019-12-18  6929  	}
> 6c271ce2f1d572 Jens Axboe     2019-01-10  6930  
> ee7d46d9db19de Pavel Begunkov 2019-12-30  6931  	/* make sure SQ entry isn't read before tail */
> ee7d46d9db19de Pavel Begunkov 2019-12-30  6932  	nr = min3(nr, ctx->sq_entries, io_sqring_entries(ctx));
> 9ef4f124894b7b Pavel Begunkov 2019-12-30  6933  
> 2b85edfc0c90ef Pavel Begunkov 2019-12-28  6934  	if (!percpu_ref_tryget_many(&ctx->refs, nr))
> 2b85edfc0c90ef Pavel Begunkov 2019-12-28  6935  		return -EAGAIN;
> 6c271ce2f1d572 Jens Axboe     2019-01-10  6936  
> d8a6df10aac9f2 Jens Axboe     2020-10-15  6937  	percpu_counter_add(&current->io_uring->inflight, nr);
> faf7b51c06973f Jens Axboe     2020-10-07  6938  	refcount_add(nr, &current->usage);
> 6c271ce2f1d572 Jens Axboe     2019-01-10  6939  
> ba88ff112bdfde Pavel Begunkov 2021-02-10  6940  	io_submit_state_start(&ctx->submit_state, nr);
> 863e05604a6fb4 Pavel Begunkov 2020-10-27  6941  	link.head = NULL;
> b14cca0c84c760 Pavel Begunkov 2020-01-17  6942  
> 6c271ce2f1d572 Jens Axboe     2019-01-10  6943  	for (i = 0; i < nr; i++) {
> 3529d8c2b353e6 Jens Axboe     2019-12-19  6944  		const struct io_uring_sqe *sqe;
> 196be95cd55720 Pavel Begunkov 2019-11-07  6945  		struct io_kiocb *req;
> 1cb1edb2f5ba8a Pavel Begunkov 2020-02-06  6946  		int err;
> fb5ccc98782f65 Pavel Begunkov 2019-10-25  6947  
> b1e50e549b1372 Pavel Begunkov 2020-04-08  6948  		sqe = io_get_sqe(ctx);
> b1e50e549b1372 Pavel Begunkov 2020-04-08  6949  		if (unlikely(!sqe)) {
> b1e50e549b1372 Pavel Begunkov 2020-04-08  6950  			io_consume_sqe(ctx);
> b1e50e549b1372 Pavel Begunkov 2020-04-08  6951  			break;
> b1e50e549b1372 Pavel Begunkov 2020-04-08  6952  		}
> 258b29a93bfe74 Pavel Begunkov 2021-02-10  6953  		req = io_alloc_req(ctx);
> 196be95cd55720 Pavel Begunkov 2019-11-07  6954  		if (unlikely(!req)) {
> 196be95cd55720 Pavel Begunkov 2019-11-07  6955  			if (!submitted)
> 196be95cd55720 Pavel Begunkov 2019-11-07  6956  				submitted = -EAGAIN;
> fb5ccc98782f65 Pavel Begunkov 2019-10-25  6957  			break;
> 196be95cd55720 Pavel Begunkov 2019-11-07  6958  		}
> 709b302faddfac Pavel Begunkov 2020-04-08  6959  		io_consume_sqe(ctx);
> d3656344fea033 Jens Axboe     2019-12-18  6960  		/* will complete beyond this point, count as submitted */
> d3656344fea033 Jens Axboe     2019-12-18  6961  		submitted++;
> d3656344fea033 Jens Axboe     2019-12-18  6962  
> 258b29a93bfe74 Pavel Begunkov 2021-02-10  6963  		err = io_init_req(ctx, req, sqe);
> ef4ff581102a91 Pavel Begunkov 2020-04-12  6964  		if (unlikely(err)) {
> 1cb1edb2f5ba8a Pavel Begunkov 2020-02-06  6965  fail_req:
> e1e16097e265da Jens Axboe     2020-06-22  6966  			io_put_req(req);
> e1e16097e265da Jens Axboe     2020-06-22  6967  			io_req_complete(req, err);
> fb5ccc98782f65 Pavel Begunkov 2019-10-25  6968  			break;
> 196be95cd55720 Pavel Begunkov 2019-11-07  6969  		}
> fb5ccc98782f65 Pavel Begunkov 2019-10-25  6970  
> 354420f705ccd0 Jens Axboe     2020-01-08  6971  		trace_io_uring_submit_sqe(ctx, req->opcode, req->user_data,
> 2d7e935809b7f7 Pavel Begunkov 2021-01-19  6972  					true, ctx->flags & IORING_SETUP_SQPOLL);
> c5eef2b9449ba2 Pavel Begunkov 2021-02-10  6973  		err = io_submit_sqe(req, sqe, &link);
> 1d4240cc9e7bb1 Pavel Begunkov 2020-04-12  6974  		if (err)
> 1d4240cc9e7bb1 Pavel Begunkov 2020-04-12  6975  			goto fail_req;
> 6c271ce2f1d572 Jens Axboe     2019-01-10  6976  	}
> 6c271ce2f1d572 Jens Axboe     2019-01-10  6977  
> 9466f43741bc08 Pavel Begunkov 2020-01-25  6978  	if (unlikely(submitted != nr)) {
> 9466f43741bc08 Pavel Begunkov 2020-01-25  6979  		int ref_used = (submitted == -EAGAIN) ? 0 : submitted;
> d8a6df10aac9f2 Jens Axboe     2020-10-15  6980  		struct io_uring_task *tctx = current->io_uring;
> d8a6df10aac9f2 Jens Axboe     2020-10-15  6981  		int unused = nr - ref_used;
> 9466f43741bc08 Pavel Begunkov 2020-01-25  6982  
> d8a6df10aac9f2 Jens Axboe     2020-10-15  6983  		percpu_ref_put_many(&ctx->refs, unused);
> d8a6df10aac9f2 Jens Axboe     2020-10-15  6984  		percpu_counter_sub(&tctx->inflight, unused);
> d8a6df10aac9f2 Jens Axboe     2020-10-15  6985  		put_task_struct_many(current, unused);
> 9466f43741bc08 Pavel Begunkov 2020-01-25  6986  	}
> 863e05604a6fb4 Pavel Begunkov 2020-10-27  6987  	if (link.head)
> c5eef2b9449ba2 Pavel Begunkov 2021-02-10  6988  		io_queue_link_head(link.head);
> ba88ff112bdfde Pavel Begunkov 2021-02-10  6989  	io_submit_state_end(&ctx->submit_state, ctx);
> 6c271ce2f1d572 Jens Axboe     2019-01-10  6990  
> ae9428ca61271b Pavel Begunkov 2019-11-06  6991  	 /* Commit SQ ring head once we've consumed and submitted all SQEs */
> ae9428ca61271b Pavel Begunkov 2019-11-06  6992  	io_commit_sqring(ctx);
> ae9428ca61271b Pavel Begunkov 2019-11-06  6993  
> 6c271ce2f1d572 Jens Axboe     2019-01-10  6994  	return submitted;
> 6c271ce2f1d572 Jens Axboe     2019-01-10  6995  }
> 6c271ce2f1d572 Jens Axboe     2019-01-10  6996  
> 
> :::::: The code at line 6920 was first introduced by commit
> :::::: 0f2122045b946241a9e549c2a76cea54fa58a7ff io_uring: don't rely on weak ->files references
> 
> :::::: TO: Jens Axboe <axboe@kernel.dk>
> :::::: CC: Jens Axboe <axboe@kernel.dk>
> 
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
> 

-- 
Pavel Begunkov