Re: [PATCH] usb: core: sysfs: show product, manufacturer and serial without the device lock

[sashiko-bot@kernel.org]

> From: Joe Finzel <joe@sudmix.de>
> 
> Reading the product, manufacturer or serial attribute of a USB device
> takes the device lock. A hub holds its lock in hub_event() while it
> enumerates all of its ports, including the debounce and reset delays of
> every child, so a reader of the hub's strings waits until the last port
> is done -- seconds on a hub with several devices.
> 
> udev reads these strings for every USB device (the usb_id builtin, run
> from 50-udev-default.rules). Its worker blocks SIGTERM, so when systemd
> stops udevd in the initrd before switching root, it waits for that
> worker. On a desktop with a few hubs this delays every boot:
> 
>   i7-13700K, ASUS ROG STRIX Z790-F, four hubs with HID devices behind
>   them: udevd took 1.7 s to stop, while the hubs were still enumerating.
> [ ... ]
> Andy Whitcroft reported the same boot stall in 2010 ("khubd -- switch
> USB product/manufacturer/serial handling to RCU"); back then the strings
> could still change under Wireless USB.
> 
> Signed-off-by: Joe Finzel <joe@sudmix.de>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20261011-usb-string-attrs-v1-1-81c01b035237@sudmix.de?part=1