Re: [Suspend-devel] [BUG] 3.7-rc regression bisected: s2disk fails to resume image: Processes could not be frozen, cannot continue resuming

Pavel Machek
2013-09-24T00:21:15Z

Hi!

> > And from suspend_ioctls.h:
> > #define SNAPSHOT_IOC_MAGIC '3'
> > #define SNAPSHOT_FREEZE _IO(SNAPSHOT_IOC_MAGIC, 1)
> >
> > My mistake, should be '3' instead of 3.
>
> OK... The thing to test, then, is what does __usermodehelper_disable()
> return to freeze_processes(). If that's where this -EAGAIN comes from,
> we at least have a plausible theory re what's going on.
>
> freeze_processes() uses __usermodehelper_disable() to stop any new userland
> processes spawned by UMH (modprobe, etc.) and waits for ones it might be
> waiting for to complete. Then it does try_to_freeze_tasks(), which
> freezes remaining userland, carefully skipping the current thread.
> However, it misses the possibility that current thread might have been
> spawned by something that had been launched by UMH, with UMH waiting
> for it. Which is the case of everything spawned by linuxrc.
>
> I'd try something like diff below, but I'm *NOT* familiar with swsusp at
> all; it's not for mainline until ACKed by swsusp folks.
>
> diff --git a/kernel/kmod.c b/kernel/kmod.c
> index fb32636..d968882 100644
> --- a/kernel/kmod.c
> +++ b/kernel/kmod.c
> @@ -571,7 +571,8 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
> DECLARE_COMPLETION_ONSTACK(done);
> int retval = 0;
>
> - helper_lock();
> + if (!(current->flags & PF_FREEZER_SKIP))
> + helper_lock();
> if (!khelper_wq || usermodehelper_disabled) {
> retval = -EBUSY;
> goto out;
> @@ -611,7 +612,8 @@ wait_done:
> out:
> call_usermodehelper_freeinfo(sub_info);
> unlock:
> - helper_unlock();
> + if (!(current->flags & PF_FREEZER_SKIP))
> + helper_unlock();
> return retval;
> }
> EXPORT_SYMBOL(call_usermodehelper_exec);

PF_FREEZER_SKIP flag is manipulated at about 1000 places, so I'm not
sure this will nest correctly. They seem to be in form of

|= FREEZER_SKIP
schedule()
&= ~FREEZER_SKIP

so this should be safe, but...

Pavel
--
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