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SubjectRe: [PATCH] init: no need to wait device probe
From
Date
Hi,

On 03/15/2018 12:20 AM, ning.a.zhang@intel.com wrote:
> From: Zhang Ning <ning.a.zhang@intel.com>

meta comment (i.e., not about the merits of the patch itself):

You'll need to send the patch to someone if you want it to be merged.
Maintainers don't mine mailing lists for patches to apply.

> there are 2 reasons for no need to wait device probe
>
> reason 1:
> mount root device is very late in kernel initial stage.
> all initcalls are finished. that means most of probe functions
> are returned.
>
> and deferred probe are also finished by late_initcall.
> only async probe driver are possible in probing.
>
> no block devices, device-mapper or nfs are use async probe.
> so no need to wait device probe.
>
> reason 2:
> let's check dd.c, probe_count is increased and decreased only
> in really_probe, and when really_probe returns, probe_count
> always be 0.
>
> when someone really wants to wait device-B probe.
> but code looks like:
>
> thread-1: thread-2:
> probe device-A; wait_for_device_probe();
> msleep(30);
> probe device-B
>
> when device-A probe finishes, thread-2 will be wakeup,
> but device-B is not probed.
>
> wait_for_device_probe can't make sure the device you want is probed.
>
> based on above 2 reasons, no need to wait for device probe.
>
> Signed-off-by: Zhang Ning <ning.a.zhang@intel.com>
> ---
> init/do_mounts.c | 9 ---------
> init/do_mounts_md.c | 2 --
> 2 files changed, 11 deletions(-)
>
> diff --git a/init/do_mounts.c b/init/do_mounts.c
> index 7cf4f6dafd5f..a9fb2ad44964 100644
> --- a/init/do_mounts.c
> +++ b/init/do_mounts.c
> @@ -555,15 +555,6 @@ void __init prepare_namespace(void)
> ssleep(root_delay);
> }
>
> - /*
> - * wait for the known devices to complete their probing
> - *
> - * Note: this is a potential source of long boot delays.
> - * For example, it is not atypical to wait 5 seconds here
> - * for the touchpad of a laptop to initialize.
> - */
> - wait_for_device_probe();
> -
> md_run_setup();
>
> if (saved_root_name[0]) {
> diff --git a/init/do_mounts_md.c b/init/do_mounts_md.c
> index 3f733c760a8c..4aab3492e71d 100644
> --- a/init/do_mounts_md.c
> +++ b/init/do_mounts_md.c
> @@ -292,8 +292,6 @@ static void __init autodetect_raid(void)
> printk(KERN_INFO "md: Waiting for all devices to be available before autodetect\n");
> printk(KERN_INFO "md: If you don't use raid, use raid=noautodetect\n");
>
> - wait_for_device_probe();
> -
> fd = sys_open("/dev/md0", 0, 0);
> if (fd >= 0) {
> sys_ioctl(fd, RAID_AUTORUN, raid_autopart);
>


--
~Randy

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