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([2600:1700:e321:62f0:da43:aeff:fecc:bfd5]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2ee0fad0797sm2141990a91.40.2024.11.27.14.48.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 27 Nov 2024 14:48:08 -0800 (PST) Sender: Guenter Roeck Message-ID: <1bdc12d6-ac23-49ff-a235-5ea54ca2ddaa@roeck-us.net> Date: Wed, 27 Nov 2024 14:48:06 -0800 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [net-next v6 5/9] net: napi: Add napi_config To: Joe Damato , netdev@vger.kernel.org, mkarsten@uwaterloo.ca, skhawaja@google.com, sdf@fomichev.me, bjorn@rivosinc.com, amritha.nambiar@intel.com, sridhar.samudrala@intel.com, willemdebruijn.kernel@gmail.com, edumazet@google.com, Jakub Kicinski , "David S. Miller" , Paolo Abeni , Jonathan Corbet , Jiri Pirko , Sebastian Andrzej Siewior , Lorenzo Bianconi , Johannes Berg , "open list:DOCUMENTATION" , open list , pcnet32@frontier.com References: <20241011184527.16393-1-jdamato@fastly.com> <20241011184527.16393-6-jdamato@fastly.com> <85dd4590-ea6b-427d-876a-1d8559c7ad82@roeck-us.net> Content-Language: en-US From: Guenter Roeck Autocrypt: addr=linux@roeck-us.net; keydata= xsFNBE6H1WcBEACu6jIcw5kZ5dGeJ7E7B2uweQR/4FGxH10/H1O1+ApmcQ9i87XdZQiB9cpN RYHA7RCEK2dh6dDccykQk3bC90xXMPg+O3R+C/SkwcnUak1UZaeK/SwQbq/t0tkMzYDRxfJ7 nyFiKxUehbNF3r9qlJgPqONwX5vJy4/GvDHdddSCxV41P/ejsZ8PykxyJs98UWhF54tGRWFl 7i1xvaDB9lN5WTLRKSO7wICuLiSz5WZHXMkyF4d+/O5ll7yz/o/JxK5vO/sduYDIlFTvBZDh gzaEtNf5tQjsjG4io8E0Yq0ViobLkS2RTNZT8ICq/Jmvl0SpbHRvYwa2DhNsK0YjHFQBB0FX IdhdUEzNefcNcYvqigJpdICoP2e4yJSyflHFO4dr0OrdnGLe1Zi/8Xo/2+M1dSSEt196rXaC kwu2KgIgmkRBb3cp2vIBBIIowU8W3qC1+w+RdMUrZxKGWJ3juwcgveJlzMpMZNyM1jobSXZ0 VHGMNJ3MwXlrEFPXaYJgibcg6brM6wGfX/LBvc/haWw4yO24lT5eitm4UBdIy9pKkKmHHh7s jfZJkB5fWKVdoCv/omy6UyH6ykLOPFugl+hVL2Prf8xrXuZe1CMS7ID9Lc8FaL1ROIN/W8Vk BIsJMaWOhks//7d92Uf3EArDlDShwR2+D+AMon8NULuLBHiEUQARAQABzTJHdWVudGVyIFJv ZWNrIChMaW51eCBhY2NvdW50KSA8bGludXhAcm9lY2stdXMubmV0PsLBgQQTAQIAKwIbAwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4ACGQEFAlVcphcFCRmg06EACgkQyx8mb86fmYFg0RAA nzXJzuPkLJaOmSIzPAqqnutACchT/meCOgMEpS5oLf6xn5ySZkl23OxuhpMZTVX+49c9pvBx hpvl5bCWFu5qC1jC2eWRYU+aZZE4sxMaAGeWenQJsiG9lP8wkfCJP3ockNu0ZXXAXwIbY1O1 c+l11zQkZw89zNgWgKobKzrDMBFOYtAh0pAInZ9TSn7oA4Ctejouo5wUugmk8MrDtUVXmEA9 7f9fgKYSwl/H7dfKKsS1bDOpyJlqhEAH94BHJdK/b1tzwJCFAXFhMlmlbYEk8kWjcxQgDWMu GAthQzSuAyhqyZwFcOlMCNbAcTSQawSo3B9yM9mHJne5RrAbVz4TWLnEaX8gA5xK3uCNCeyI sqYuzA4OzcMwnnTASvzsGZoYHTFP3DQwf2nzxD6yBGCfwNGIYfS0i8YN8XcBgEcDFMWpOQhT Pu3HeztMnF3HXrc0t7e5rDW9zCh3k2PA6D2NV4fews9KDFhLlTfCVzf0PS1dRVVWM+4jVl6l HRIAgWp+2/f8dx5vPc4Ycp4IsZN0l1h9uT7qm1KTwz+sSl1zOqKD/BpfGNZfLRRxrXthvvY8 BltcuZ4+PGFTcRkMytUbMDFMF9Cjd2W9dXD35PEtvj8wnEyzIos8bbgtLrGTv/SYhmPpahJA l8hPhYvmAvpOmusUUyB30StsHIU2LLccUPPOwU0ETofVZwEQALlLbQeBDTDbwQYrj0gbx3bq 7kpKABxN2MqeuqGr02DpS9883d/t7ontxasXoEz2GTioevvRmllJlPQERVxM8gQoNg22twF7 pB/zsrIjxkE9heE4wYfN1AyzT+AxgYN6f8hVQ7Nrc9XgZZe+8IkuW/Nf64KzNJXnSH4u6nJM J2+Dt274YoFcXR1nG76Q259mKwzbCukKbd6piL+VsT/qBrLhZe9Ivbjq5WMdkQKnP7gYKCAi pNVJC4enWfivZsYupMd9qn7Uv/oCZDYoBTdMSBUblaLMwlcjnPpOYK5rfHvC4opxl+P/Vzyz 6WC2TLkPtKvYvXmdsI6rnEI4Uucg0Au/Ulg7aqqKhzGPIbVaL+U0Wk82nz6hz+WP2ggTrY1w ZlPlRt8WM9w6WfLf2j+PuGklj37m+KvaOEfLsF1v464dSpy1tQVHhhp8LFTxh/6RWkRIR2uF I4v3Xu/k5D0LhaZHpQ4C+xKsQxpTGuYh2tnRaRL14YMW1dlI3HfeB2gj7Yc8XdHh9vkpPyuT nY/ZsFbnvBtiw7GchKKri2gDhRb2QNNDyBnQn5mRFw7CyuFclAksOdV/sdpQnYlYcRQWOUGY HhQ5eqTRZjm9z+qQe/T0HQpmiPTqQcIaG/edgKVTUjITfA7AJMKLQHgp04Vylb+G6jocnQQX JqvvP09whbqrABEBAAHCwWUEGAECAA8CGwwFAlVcpi8FCRmg08MACgkQyx8mb86fmYHNRQ/+ J0OZsBYP4leJvQF8lx9zif+v4ZY/6C9tTcUv/KNAE5leyrD4IKbnV4PnbrVhjq861it/zRQW cFpWQszZyWRwNPWUUz7ejmm9lAwPbr8xWT4qMSA43VKQ7ZCeTQJ4TC8kjqtcbw41SjkjrcTG wF52zFO4bOWyovVAPncvV9eGA/vtnd3xEZXQiSt91kBSqK28yjxAqK/c3G6i7IX2rg6pzgqh hiH3/1qM2M/LSuqAv0Rwrt/k+pZXE+B4Ud42hwmMr0TfhNxG+X7YKvjKC+SjPjqp0CaztQ0H nsDLSLElVROxCd9m8CAUuHplgmR3seYCOrT4jriMFBtKNPtj2EE4DNV4s7k0Zy+6iRQ8G8ng QjsSqYJx8iAR8JRB7Gm2rQOMv8lSRdjva++GT0VLXtHULdlzg8VjDnFZ3lfz5PWEOeIMk7Rj trjv82EZtrhLuLjHRCaG50OOm0hwPSk1J64R8O3HjSLdertmw7eyAYOo4RuWJguYMg5DRnBk WkRwrSuCn7UG+qVWZeKEsFKFOkynOs3pVbcbq1pxbhk3TRWCGRU5JolI4ohy/7JV1TVbjiDI HP/aVnm6NC8of26P40Pg8EdAhajZnHHjA7FrJXsy3cyIGqvg9os4rNkUWmrCfLLsZDHD8FnU mDW4+i+XlNFUPUYMrIKi9joBhu18ssf5i5Q= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/27/24 12:00, Joe Damato wrote: > On Wed, Nov 27, 2024 at 10:51:16AM -0800, Joe Damato wrote: >> On Wed, Nov 27, 2024 at 09:43:54AM -0800, Guenter Roeck wrote: >>> Hi, >>> >>> On Fri, Oct 11, 2024 at 06:45:00PM +0000, Joe Damato wrote: >>>> Add a persistent NAPI config area for NAPI configuration to the core. >>>> Drivers opt-in to setting the persistent config for a NAPI by passing an >>>> index when calling netif_napi_add_config. >>>> >>>> napi_config is allocated in alloc_netdev_mqs, freed in free_netdev >>>> (after the NAPIs are deleted). >>>> >>>> Drivers which call netif_napi_add_config will have persistent per-NAPI >>>> settings: NAPI IDs, gro_flush_timeout, and defer_hard_irq settings. >>>> >>>> Per-NAPI settings are saved in napi_disable and restored in napi_enable. >>>> >>>> Co-developed-by: Martin Karsten >>>> Signed-off-by: Martin Karsten >>>> Signed-off-by: Joe Damato >>>> Reviewed-by: Jakub Kicinski >>> >>> This patch triggers a lock inversion message on pcnet Ethernet adapters. >> >> Thanks for the report. I am not familiar with the pcnet driver, but >> took some time now to read the report below and the driver code. >> >> I could definitely be reading the output incorrectly (if so please >> let me know), but it seems like the issue can be triggered in this >> case: > > Sorry, my apologies, I both: > - read the report incorrectly, and > - proposed a bad patch that would result in a deadlock :) > > After re-reading it and running this by Martin (who is CC'd), the > inversion is actually: > > CPU 0: > pcnet32_open > lock(lp->lock) > napi_enable > napi_hash_add <- before this executes, CPU 1 proceeds > lock(napi_hash_lock) > CPU 1: > pcnet32_close > napi_disable > napi_hash_del > lock(napi_hash_lock) > < INTERRUPT > > pcnet32_interrupt > lock(lp->lock) > > This is now an inversion because: > > CPU 0: holds lp->lock and is about to take napi_hash_lock > CPU 1: holds napi_hashlock and an IRQ firing on CPU 1 tries to take > lp->lock (which CPU 0 already holds) > > Neither side can proceed: > - CPU 0 is stuck waiting for napi_hash_lock > - CPU 1 is stuck waiting for lp->lock > > I think the below explanation is still correct as to why the > identified commit causes the issue: > >> It seems this was triggered because before the identified commit, >> napi_enable did not call napi_hash_add (and thus did not take the >> napi_hash_lock). > > However, the previous patch I proposed for pcnet32 would also cause > a deadlock as the watchdog timer's function also needs lp->lock. > > A corrected patch for pcnet32 can be found below. > > Guenter: Sorry, would you mind testing the below instead of the > previous patch? > > Don: Let me know what you think about the below? > > Netdev maintainers, there is an alternate locking solution I can > propose as an RFC that might avoid this class of problem if this > sort of issue is more widespread than just pcnet32: > - add the NAPI to the hash in netif_napi_add_weight (instead of napi_enable) > - remove the NAPI from the hash in __netif_napi_del (instead of > napi_disable) > > If changing the locking order in core is the desired route, than the > patch below should be unnecessary, but: > > diff --git a/drivers/net/ethernet/amd/pcnet32.c b/drivers/net/ethernet/amd/pcnet32.c > index 72db9f9e7bee..2e0077e68883 100644 > --- a/drivers/net/ethernet/amd/pcnet32.c > +++ b/drivers/net/ethernet/amd/pcnet32.c > @@ -2625,11 +2625,10 @@ static int pcnet32_close(struct net_device *dev) > > del_timer_sync(&lp->watchdog_timer); > > + spin_lock_irqsave(&lp->lock, flags); > netif_stop_queue(dev); > napi_disable(&lp->napi); > That is what I did, actually. Problem with that is that napi_disable() wants to be able to sleep, thus the above triggers: BUG: sleeping function called from invalid context at net/core/dev.c:6775 in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 1817, name: ip preempt_count: 1, expected: 0 2 locks held by ip/1817: #0: ffffffff81ded990 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_newlink+0x22a/0x74c #1: ff6000000498ccb0 (&lp->lock){-.-.}-{3:3}, at: pcnet32_close+0x40/0x126 irq event stamp: 3720 hardirqs last enabled at (3719): [] _raw_spin_unlock_irqrestore+0x54/0x62 hardirqs last disabled at (3720): [] _raw_spin_lock_irqsave+0x5e/0x64 softirqs last enabled at (3712): [] handle_softirqs+0x3e6/0x4a2 softirqs last disabled at (3631): [] __do_softirq+0x12/0x1a CPU: 0 UID: 0 PID: 1817 Comm: ip Tainted: G N 6.12.0-10313-g7d4050728c83-dirty #1 Tainted: [N]=TEST Hardware name: riscv-virtio,qemu (DT) Call Trace: [] dump_backtrace+0x1c/0x24 [] show_stack+0x2c/0x38 [] dump_stack_lvl+0x74/0xac [] dump_stack+0x14/0x1c [] __might_resched+0x23e/0x248 [] __might_sleep+0x3e/0x62 [] napi_disable+0x24/0x10c [] pcnet32_close+0x6c/0x126 Guenter