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SubjectRe: linux-next: umh: fix processed error when UMH_WAIT_PROC is used seems to break linux bridge on s390x (bisected)
On Fri, Jun 26, 2020 at 02:54:10AM +0000, Luis Chamberlain wrote:
> On Wed, Jun 24, 2020 at 08:37:55PM +0200, Christian Borntraeger wrote:
> >
> >
> > On 24.06.20 20:32, Christian Borntraeger wrote:
> > [...]>
> > > So the translations look correct. But your change is actually a sematic change
> > > if(ret) will only trigger if there is an error
> > > if (KWIFEXITED(ret)) will always trigger when the process ends. So we will always overwrite -ECHILD
> > > and we did not do it before.
> > >
> >
> > So the right fix is
> >
> > diff --git a/kernel/umh.c b/kernel/umh.c
> > index f81e8698e36e..a3a3196e84d1 100644
> > --- a/kernel/umh.c
> > +++ b/kernel/umh.c
> > @@ -154,7 +154,7 @@ static void call_usermodehelper_exec_sync(struct subprocess_info *sub_info)
> > * the real error code is already in sub_info->retval or
> > * sub_info->retval is 0 anyway, so don't mess with it then.
> > */
> > - if (KWIFEXITED(ret))
> > + if (KWEXITSTATUS(ret))
> > sub_info->retval = KWEXITSTATUS(ret);
> > }
> >
> > I think.
>
> Nope, the right form is to check for WIFEXITED() before using WEXITSTATUS().
> I'm not able to reproduce this on x86 with a bridge. What type of bridge
> are you using on a guest, or did you mean using KVM so that the *host*
> can spawn kvm guests?
>
> It would be good if you can try to add a bridge manually and see where
> things fail. Can you do something like this:
>
> brctl addbr br0
> brctl addif br0 ens6
> ip link set dev br0 up
>
> Note that most callers are for modprobe. I'd be curious to see which
> umh is failing which breaks bridge for you. Can you trut this so we can
> see which umh call is failing?

Christian, any luck getting to test the code below to see what this
reveals?

Luis

>
> diff --git a/kernel/umh.c b/kernel/umh.c
> index f81e8698e36e..5ad74bc301d8 100644
> --- a/kernel/umh.c
> +++ b/kernel/umh.c
> @@ -2,6 +2,9 @@
> /*
> * umh - the kernel usermode helper
> */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> #include <linux/module.h>
> #include <linux/sched.h>
> #include <linux/sched/task.h>
> @@ -154,8 +157,12 @@ static void call_usermodehelper_exec_sync(struct subprocess_info *sub_info)
> * the real error code is already in sub_info->retval or
> * sub_info->retval is 0 anyway, so don't mess with it then.
> */
> - if (KWIFEXITED(ret))
> + printk("== ret: %02x\n", ret);
> + printk("== KWIFEXITED(ret): %02x\n", KWIFEXITED(ret));
> + if (KWIFEXITED(ret)) {
> + printk("KWEXITSTATUS(ret): %d\n", KWEXITSTATUS(ret));
> sub_info->retval = KWEXITSTATUS(ret);
> + }
> }
>
> /* Restore default kernel sig handler */
> @@ -383,6 +390,7 @@ struct subprocess_info *call_usermodehelper_setup(const char *path, char **argv,
> void *data)
> {
> struct subprocess_info *sub_info;
> + unsigned int i = 0;
> sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
> if (!sub_info)
> goto out;
> @@ -394,6 +402,11 @@ struct subprocess_info *call_usermodehelper_setup(const char *path, char **argv,
> #else
> sub_info->path = path;
> #endif
> + pr_info("sub_info->path: %s\n", sub_info->path);
> + while (argv[i])
> + printk(KERN_INFO "%s ", argv[i++]);
> + printk(KERN_INFO "\n");
> +
> sub_info->argv = argv;
> sub_info->envp = envp;
>
>

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