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SubjectRe: [PATCH 7/7] initdev:kernel:Await block device discovery
David VomLehn wrote:
> --- a/init/do_mounts.c
> +++ b/init/do_mounts.c
> @@ -358,6 +358,18 @@ void __init mount_root(void)
> #endif
> }
>
> +/**
> + * root_present - determine whether the root device is available yet
> + *
> + * Returns true if the root device is available, false if not. The check to
> + * see if the root device is available is done by check to see whether it
> + * has been assigned a major/minor device number.
> + */
> +static bool root_present(void)
> +{
> + return name_to_dev_t(saved_root_name) != 0;
> +}
> +
> /*
> * Prepare the namespace - decide what/where to mount, load ramdisks, etc.
> */
> @@ -398,12 +410,21 @@ void __init prepare_namespace(void)
> goto out;
>
> /* wait for any asynchronous scanning to complete */
> - if ((ROOT_DEV == 0) && root_wait) {
> + if (ROOT_DEV == 0) {
> printk(KERN_INFO "Waiting for root device %s...\n",
> saved_root_name);
> - while (driver_probe_done() != 0 ||
> - (ROOT_DEV = name_to_dev_t(saved_root_name)) == 0)
> - msleep(100);
> + if (root_wait) {
> + while (driver_probe_done() != 0 ||
> + (ROOT_DEV = name_to_dev_t(saved_root_name)) ==
> + 0)
> + msleep(100);
> + }
> +
> + else {
> + initdev_wait(INITDEV_BLOCK_TYPE, root_present);
> + ROOT_DEV = name_to_dev_t(saved_root_name);
> + }
> +
> async_synchronize_full();
> }
>

This together with 1/7, 5/7, 6/7 looks seriously flawed, if not broken.

1.) It depends on the rootdelay so big that it is guaranteed that one
or more initdev_found() have been called before prepare_namespace()'s
ssleep(root_delay) is over. This is because initdev_wait() does not
wait at all if called when the number of pending initdevs is 0.

Hence the whole thing, as currently implemented, is quite useless: The
user/admin has to guess what a safe rootdelay value is, and then the
kernel will always be delayed for >= rootdelay.

2.) The fact that initdev_wait() does not wait at all when there are no
pending initdevs causes another failure. If there are sequences of the
following type:

initdev_found(INITDEV_BLOCK_TYPE);
initdev_probe_done(INITDEV_BLOCK_TYPE); /* found other dev */
initdev_found(INITDEV_BLOCK_TYPE);
initdev_probe_done(INITDEV_BLOCK_TYPE); /* found root dev */

then prepare_namespace() will fall through without ROOT_DEV found and
booting will fail, won't it?

I suspect that there are similar problems with the console and
networking parts of the patch series.
--
Stefan Richter
-=====-==--= -==- --==-
http://arcgraph.de/sr/


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