linux-kernel - Re: [PATCH] nvme: Let the blocklayer set timeouts for requests

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Message-ID: <20251202-78-chops-11b0312d@mheyne-amazon>
Date: Tue, 2 Dec 2025 17:51:36 +0000
From: "Heyne, Maximilian" <mheyne@...zon.de>
To: Keith Busch <kbusch@...nel.org>
CC: Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>, "Sagi
 Grimberg" <sagi@...mberg.me>, "linux-nvme@...ts.infradead.org"
	<linux-nvme@...ts.infradead.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] nvme: Let the blocklayer set timeouts for requests

On Tue, Dec 02, 2025 at 10:39:11AM -0700, Keith Busch wrote:
> On Tue, Dec 02, 2025 at 01:58:19PM +0000, Heyne, Maximilian wrote:
> > When initializing an nvme request which is about to be send to the block
> > layer, we do not need to initialize its timeout. If it's left
> > uninitialized at 0 the block layer will use the request queue's timeout
> > in blk_add_timer (via nvme_start_request which is called from
> > nvme_*_queue_rq). These timeouts are setup to either NVME_IO_TIMEOUT or
> > NVME_ADMIN_TIMEOUT when the request queues were created.
> > 
> > Because the io_timeout of the IO queues can actually be modified via
> > sysfs, the following situation can occur:
> > 
> > 1) NVME_IO_TIMEOUT = 30 (default module parameter)
> > 2) nvme1n1 is probed. IO queues default timeout is 30 s
> > 3) manually change the IO timeout to 90 s
> >    echo 90000 > /sys/class/nvme/nvme1/nvme1n1/queue/io_timeout
> > 4) nvme zns report-zones /dev/nvme1n1
> >    This command issues IO commands with timeout 30 s instead of the
> >    wanted 90 s which might be more suitable for this device.
> 
> Does this example really use 30s, though? User space commands should be
> going through nvme_submit_user_cmd(), which overrides the timeout set
> from the nvme_init_request with whatever the user requested (usually 0).

You're right. I actually worked on multiple (older) kernel versions and
forgot about this case. It was actually commit 470e900c8036ff ("nvme:
refactor nvme_alloc_request") which subtly changed the behavior but only
for the ioctl case. So ioctl's are fine then but, for example,
everything which goes via nvme_submit_sync_cmd shows the issue. So we
need to update the commit message accordingly. Sorry for that. I'll give
it a day or two for further comments on this patch and then send it with
a more correct message.



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