lkml.org 
[lkml]   [2012]   [Mar]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] firmware loader: don't cancel _nowait requests when helper is not yet available
    On 03/14/12 16:13, Rafael J. Wysocki wrote:
    > On Thursday, March 15, 2012, Rafael J. Wysocki wrote:
    >> On Wednesday, March 14, 2012, Stephen Boyd wrote:
    >>> On 03/13/12 13:14, Rafael J. Wysocki wrote:
    >>>> All of those use cases are in fact of the "wait for user space to be thawed
    >>>> and then load the firmware" type, which I believe may be handled without
    >>>> changing that code.
    >>>>
    >>>> Why don't you make your kthread freezable, for one example?
    >>>>
    >>>> Why don't you use a freezable workqueue instead?
    >>>>
    >>> If we put it on the freezable workqueue or make it a freezable thread
    >>> will it work?
    >> That depends on what exactly you want to achieve, which isn't entirely clear
    >> to me at this point.
    >>
    >>> In my scenario a wakeup interrupt comes in that wakes us up from
    >>> suspend. Within that wakeup handler a work item is scheduled to the
    >>> freezable workqueue. That work item then calls request_firmware().
    >> That should work.
    >>
    >>> It looks like we call schedule() after thawing the workqueues and tasks
    >>> so the work item could run before usermodehelpers are enabled and then
    >>> request_firmware() would fail. Do we need something like this (ignore
    >>> the fact that we call usermodhelper_enable() twice)?
    >>>
    >>> diff --git a/kernel/power/process.c b/kernel/power/process.c
    >>> index 7e42645..61bfa95 100644
    >>> --- a/kernel/power/process.c
    >>> +++ b/kernel/power/process.c
    >>> @@ -187,6 +187,7 @@ void thaw_processes(void)
    >>> } while_each_thread(g, p);
    >>> read_unlock(&tasklist_lock);
    >>>
    >>> + usermodehelper_enable();
    >> That would be a reasonable change.
    >>
    >>> schedule();
    >>> printk("done.\n");
    >>> }
    >>>
    >>>
    >>> Is there a reason we disable usermodehelpers if
    >>> CONFIG_SUSPEND_FREEZER=n?
    >> Not really, but CONFIG_SUSPEND_FREEZER=n can only work reliably in a
    >> very limited set of cases, so I don't think it's even worth making the
    >> general code depend on it.
    >>
    >> I'd actually prefer to remove CONFIG_SUSPEND_FREEZER altogether,
    >> because it's not very useful nowadays (probably isn't useful at all).
    >>
    >>> Should we do this instead so that
    >>> usermodehelpers are only disabled if we freeze userspace? Also what is
    >>> that schedule() call in thaw_kernel_threads() for? It looks like we'll
    >>> call schedule between kernel thread thawing and userspace thawing.
    >> Which is OK, I think.
    > Moreover, thaw_kernel_threads() is _only_ called by (a) freeze_kernel_threads()
    > on error and (b) user-space hibernate interface in kernel/power/user.c
    > (and please read the comment in there describing what it's there for, which
    > also explains why the schedule() call in there is necessary).

    Exactly. So in case (a) when the error occurs we'll have this call flow:

    usermodehelpers_disable()
    suspend_freeze_processes()
    freeze_processes()
    freeze_kernel_threads()
    try_to_freeze_tasks() <-- returns error
    thaw_kernel_threads()
    schedule()
    thaw_processes()
    usermodehelpers_enable()

    Shouldn't we schedule only after we thaw all processes (not just tasks)?
    Otherwise we may run a kernel thread before userspace is thawed?

    --
    Sent by an employee of the Qualcomm Innovation Center, Inc.
    The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.



    \
     
     \ /
      Last update: 2012-03-15 00:19    [W:4.285 / U:0.880 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site