[PATCH] init: no need to wait device probe

From: ning . a . zhang
Date: Thu Mar 15 2018 - 03:20:46 EST


From: Zhang Ning <ning.a.zhang@xxxxxxxxx>

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@xxxxxxxxx>
---
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);
--
2.14.2