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([2a0b:e7c0:0:107::aaaa:69]) by smtp.gmail.com with ESMTPSA id dq16-20020a170907735000b00a524318c380sm5417547ejc.80.2024.04.22.00.29.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 22 Apr 2024 00:29:38 -0700 (PDT) Message-ID: Date: Mon, 22 Apr 2024 09:29:37 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net,v3] net: ppp: Fix deadlock caused by unsafe-irq lock in ap_get() To: Jeongjun Park Cc: davem@davemloft.net, edumazet@google.com, gregkh@linuxfoundation.org, kuba@kernel.org, linux-kernel@vger.kernel.org, linux-ppp@vger.kernel.org, netdev@vger.kernel.org, pabeni@redhat.com, syzbot+393d0ef63475d9bb1f16@syzkaller.appspotmail.com, syzkaller-bugs@googlegroups.com References: <0032f249-7787-4875-a782-0847c04d5c9c@kernel.org> <20240422071858.140237-1-aha310510@gmail.com> Content-Language: en-US From: Jiri Slaby Autocrypt: addr=jirislaby@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 22. 04. 24, 9:18, Jeongjun Park wrote: > ======================================================== > WARNING: possible irq lock inversion dependency detected > 6.8.0-rc3-syzkaller-00041-g547ab8fc4cb0 #0 Not tainted > -------------------------------------------------------- .. > ... key at: [] port_lock_key+0x0/0x20 > ... acquired at: > lock_acquire+0x1e3/0x530 kernel/locking/lockdep.c:5754 > __raw_read_lock include/linux/rwlock_api_smp.h:150 [inline] > _raw_read_lock+0x36/0x50 kernel/locking/spinlock.c:228 > ap_get drivers/net/ppp/ppp_async.c:136 [inline] > ppp_asynctty_wakeup+0x20/0x210 drivers/net/ppp/ppp_async.c:352 > tty_wakeup+0xbb/0x100 drivers/tty/tty_io.c:523 > tty_port_default_wakeup+0xa6/0xf0 drivers/tty/tty_port.c:69 > serial8250_tx_chars+0x6ad/0x8a0 drivers/tty/serial/8250/8250_port.c:1835 > This is the stack trace for the issue causing the deadlock reported > by syzbot. I think there is definitely a problem with ap_get() and > this needs to be fixed. OK, but read_unlock_irq() is not the right way to do it. It would enable irqs unconditionally, so serial8250_tx_chars() would not thank you in the above call chain. Plus the issues Jakub had with the patch. And what about ppp_synctty? thanks, -- js suse labs