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AJvYcCW/7VRGVnOiS2+USsXrkn3Yyvt/5/84YPg7QWCvSJSvbpcf0PNkZkPhlLIK45YOc3i13x62sIAhHw==@kvack.org X-Gm-Message-State: AOJu0YwdKSYhlBDfuUsVPSfao1Ez8b3UPkyzaatMABzP6wX0eBmjhemJ GKs6XgTiI52RVYVBfridV1DDI50HRHTAhU104cwL5rGPzaERghINzzkoouPLEZ+F4SXlMahHrhL iWOoi6Yp+thmeVfZbxKJndp+4ltQK53kyL1mYsOv6 X-Gm-Gg: ASbGncsN8LRa2/cjIzWlAKM/gUeYJ7Lh2dBVSg6DBwOgIe4S11V4xWUXg65em15rdOf 1ZLKfxZFGaKHnCrhnuzKLQVlEgy/S3PB50YJuhOPsWcSFRAxFu/ogTkAG1U6vQA1VNHV4/6m7/I /5sIiLM2JdfKvU5dv/bHWpjw8mtZ8sEJ9SajQDRwwjxi7q9IrODeDFdvx+WSWrROA/5mhlg1y4 X-Google-Smtp-Source: AGHT+IH7QU9THUOIJXkcFhhyY5pE8ZZNfgzXLg84Ex5Q6A11Vwd6k1wi1S4TyvhsAwEvthJSpcOZcMrWncOSW4BQnNI= X-Received: by 2002:a05:622a:2284:b0:4a5:9b0f:9a54 with SMTP id d75a77b69052e-4a5a52d361amr4019381cf.18.1749047395522; Wed, 04 Jun 2025 07:29:55 -0700 (PDT) MIME-Version: 1.0 References: <68387feb.a70a0220.29d4a0.0830.GAE@google.com> <84qzzzoqkw.fsf@jogness.linutronix.de> In-Reply-To: <84qzzzoqkw.fsf@jogness.linutronix.de> From: Suren Baghdasaryan Date: Wed, 4 Jun 2025 07:29:44 -0700 X-Gm-Features: AX0GCFsIVzK9pgbt2dn3Cpgu7lCKSaLlimWGtVShPPXekcZUBUaMMXaeZ1lEQN8 Message-ID: Subject: Re: [syzbot] [mm?] possible deadlock in __vma_start_write To: John Ogness Cc: 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, Peter Zijlstra , Petr Mladek Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: E154F140019 X-Stat-Signature: w4x1dqjd9kwtqsicgn8ueoq8em6a96ys X-Rspam-User: X-HE-Tag: 1749047396-304116 X-HE-Meta: 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 vlK3opOZ I+lLpcwq1mmBhCsDokHMq1waBdrDoDP6FaymbUO/kLhJVZKZ/v95Nt/M3lGkT8i8IdX+JPWrmv47NM2HT9ozbgOYHwFnz+OPZD3aWqZEj5VVm7G9SqAGV6Cxlx3TbXi2ZHTQf 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 Wed, Jun 4, 2025 at 1:31=E2=80=AFAM John Ogness wrote: > > On 2025-06-04, Vlastimil Babka wrote: > > After consulting PeterZ on IRC, he said: > > > >> so the thing complains about: vmlock <- mapping.invalidate_lock <- bca= chefs_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 co= uld 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. Thanks for additional info, folks! I'll look into it some more to see if the chain can be broken somehow but most likely will have to live with it for now. Cheers, Suren. > > John > > [0] https://lore.kernel.org/lkml/20240603232453.33992-17-john.ogness@linu= tronix.de