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bh=d65MstfFvuzOXxquIWVaVULj0QYTs91IuDc3ZONuqOs=; b=CLy9I11uUkHUoiLMNCiMfZgRvMZYKwO56zSjtE2suePuugkT313N9CHUvtmdn/OAJXoAOl 74J0Wo08dFhwJdTCRrYvGcS+pDa2ZRJvaKoqwqq1mM4tRNFggjAGnfapYT9KdEptmk1HSa yHK1Sg6OVVOoZUx67oPZ1QhFknK0xhJ4E/sdAP74bGhvLldR6nBYaYmZpYT21Bp3GGusK2 RQ5E71bqtgAw+uNsOhoU58H8SqxTQCHjGSXQdOY7qit625Colz8swiICqEoUg6hmq4vceb /oPNlxHJ/TOBs773cZLA76hUrufYmZixbk1En4GODYDEkmWqlSN3fAU15sDtYA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1749025904; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=d65MstfFvuzOXxquIWVaVULj0QYTs91IuDc3ZONuqOs=; b=QN/ZIwAXPkroA1wzqBT0aDMNdXXdbNxfTD+attYp6//myNqdBhIG3BdjKeZW68Gj9vBi65 uG259TgMGXY49xBw== To: Vlastimil Babka , syzbot , Liam.Howlett@oracle.com, akpm@linux-foundation.org, jannh@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, pfalcato@suse.de, syzkaller-bugs@googlegroups.com Cc: Suren Baghdasaryan , Lorenzo Stoakes , Peter Zijlstra , Petr Mladek Subject: Re: [syzbot] [mm?] possible deadlock in __vma_start_write In-Reply-To: References: <68387feb.a70a0220.29d4a0.0830.GAE@google.com> Date: Wed, 04 Jun 2025 10:37:43 +0206 Message-ID: <84qzzzoqkw.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 5B31A80006 X-Stat-Signature: 5m9dpddfdzmohbxryohp1umq4cowfeem X-Rspam-User: X-HE-Tag: 1749025906-693264 X-HE-Meta: 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 l+3fqU/v B1u3bN8ipLtnd3ofnfzRz8Xk+Wet/Cib3zZ3FFEh2AUxu2lElFvbDZBmiZlLnOZpEuo5bxCFMbMLPKHEJD1UCJbVNjLqe99XnhKbTIXIY8Gn9ZXSOstAnkFTBmy5Mb24wxv+usF1SSush8vk8M2KbYbs0IyU7NnmsazrcJJ54nk5+QiFzt4kRR0y7tfeMwq0ieHfYeTCUanOtShFDuqWvyyFMcNO8RXddadVIfx9Zf68zhFxVoDasistYbr2SBX7cjUDbW//BYTP/dTPc5Qn+pNpZd7MawGxzca+HZjt8dMnK7rGA+LWOF1Q06EpyC4kqTYa0hJyE0j3U3xaQv6ebhz2C4vTGbUS9TxuFmd/+dUQYO18= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2025-06-04, Vlastimil Babka wrote: > After consulting PeterZ on IRC, he said: > >> so the thing complains about: vmlock <- mapping.invalidate_lock <- bcachefs_btree <- console_lock <- &helper->lock <- dev->mode_config.idr_mutex <- mm->mmap_lock <- vmlock > > so bcachefs is doing printk which wants console_lock, and in > drm console a possible lock chain exists that can lead to mmap lock > > To me it seems all rather theoretical, but not sure where and how we could safely > break this chain. > Hopefully one day console_lock goes away? :) It is a known problem that any caller holding a lock used by a registered legacy console will result in printk() deadlocking. This is particularly a problem with the port->lock and power management. One workaround is to enable CONFIG_PREEMPT_RT. ;-) A year ago (exactly) there was patch [0] providing a "threadprintk" boot argument that would also work around this problem. However, the only real solution is to convert the legacy consoles to nbcon. This is work in progress. John [0] https://lore.kernel.org/lkml/20240603232453.33992-17-john.ogness@linutronix.de