Re: [PATCH v2 5/5] PCI/sysfs: Use user config accessors for serial_number

[Keith Busch <kbusch@kernel.org>]

On Thu, Oct 29, 2026 at 12:20:29PM -0700, Matthew Wood wrote:
> serial_number_show() reads the device serial number with pci_get_dsn(),
> which uses the kernel config accessors which don't check
> block_cfg_access, so a read that races with a reset goes to the device
> mid-reset and can fail with -EIO or report an all-ones serial number.
> 
> Do the capability walk and DSN reads with the user config accessors
> instead, as the "config" attribute does, so each access waits for any
> pci_cfg_access_lock() holder (e.g. pci_reset_function()) to finish.
> Also wrap the reads in pci_config_pm_runtime_{get,put}() like the other
> attributes that read config space.
> 
> A reset can still start between two accesses, but the next access just
> waits for it to finish, and the DSN capability is unchanged by a reset.
> 
> Add a check that both DSN reads are successful, unlike pci_get_dsn(),
> and fail with -EIO instead of reporting an all-ones serial number if
> the device is disconnected between the capability walk and the reads.
> 
> Unlike pci_find_ext_capability(), the walk doesn't check dev->cfg_size
> first. serial_number is only visible if pci_get_dsn() found the DSN
> capability when the device was added, and cfg_size is final by then.

Looks good.

Reviewed-by: Keith Busch <kbusch@kernel.org>