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Fri, 2 Oct 2026 09:39:41 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id KheGLN17v2r3BwAAD6G6ig (envelope-from ); Fri, 02 Oct 2026 09:39:41 +0000 Message-ID: <4a4e228f-7143-4d5a-b773-2c6238852503@suse.de> Date: Fri, 2 Oct 2026 11:39:41 +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 v4 2/2] nvme-multipath: add fail_if_no_path sysfs attribute To: Krishna Iyer , kbusch@kernel.org, axboe@kernel.dk, hch@lst.de, sagi@grimberg.me Cc: linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, nilay@linux.ibm.com, saravanand@crusoe.ai, sjpark@crusoe.ai References: <20261001094857.74567-1-kiyer@crusoe.ai> <20261001094857.74567-3-kiyer@crusoe.ai> Content-Language: en-US From: Hannes Reinecke In-Reply-To: <20261001094857.74567-3-kiyer@crusoe.ai> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_SEVEN(0.00)[10]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:mid,suse.de:email,crusoe.ai:email,imap1.dmz-prg2.suse.org:helo] X-Spam-Score: -4.30 X-Spam-Level: X-Spam-Flag: NO On 10/1/26 11:48 AM, Krishna Iyer wrote: > When no usable path exists, I/O on a multipath namespace is queued > until a path returns. With ctrl_loss_tmo=-1 that can be forever: > during a long fabric outage any process waiting on the I/O is stuck in > D state. We hit this on virtualization hosts, where a SIGKILLed VM > process cannot exit while draining I/O to an unreachable NVMe/TCP > target. > > Nothing can fail this I/O without tearing something down: controller > deletion takes every namespace on the controller with it. > > Add a fail_if_no_path attribute on the ns-head disk: a persistent > per-namespace policy to fail parked and newly arriving I/O instead of > queueing it when no usable path exists. It is the namespace-scoped > counterpart to the controller-scoped fast_io_fail_tmo: the trigger is > an event userspace observes (a consumer known to be gone, for us a > SIGKILLed VM the host must reap), not a duration picked up front, and > sibling namespaces behind the same controllers keep queueing and ride > out the outage. > > A CONNECTING controller stops counting as an available path, and with > no controllers left the policy overrides the delayed_removal_secs > queue-if-no-path window; the two are opposites, so fail_if_no_path takes > precedence when both are set. ANA change and controller resetting still > queue, since both are transient. Controller state is untouched and > reconnects continue. Like dm's fail_if_no_path, the policy is transport > agnostic. > > Assisted-by: Claude:claude-fable-5 > Signed-off-by: Krishna Iyer > --- > Documentation/ABI/stable/sysfs-nvme | 16 +++++++++ > drivers/nvme/host/multipath.c | 50 +++++++++++++++++++++++++++-- > drivers/nvme/host/nvme.h | 2 ++ > drivers/nvme/host/sysfs.c | 4 ++- > 4 files changed, 69 insertions(+), 3 deletions(-) > I do get the problem, but I think that 'fail_if_no_path' is a misnomer. Problem is that we already have a 'QUEUE_IF_NO_PATH' setting, so 'FAIL_IF_NO_PATH' really sounds like the inverstion of that. Only that it isn't. Maybe rename to 'FAIL_ON_CTRL_LOSS' to make it clear that the two settings really describe different use-cases? Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich