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    SubjectRe: [PATCH] fbmem: fix race condition between register_framebuffer() and fb_open()
    On Wed, May 25, 2011 at 8:57 PM, Bruno Prémont
    <> wrote:
    > On Wed, 25 May 2011 Fabio Erculiani <> wrote:
    >> On Wed, May 25, 2011 at 8:46 PM, Bruno Prémont wrote:
    >> > On Wed, 25 May 2011 Fabio Erculiani <> wrote:
    >> >> I'm not a fbdev expert. So I leave the real fix to real men ( ;-) ).
    >> >> It is causing deadlock during boot, so I would consider it quite critical.
    >> >> Users using any fb driver will get into troubles.
    >> >> The workaround is to boot with vga=normal.
    >> >
    >> > What is your system doing during boot? I've never seen it here but maybe
    >> > my boot sequence is too simple.
    >> I'm using vesafb and vga=791. It is quite simple to reproduce.
    >> Also see:
    > Looks like gentoo kernel, might be splash is related to the hang

    Then, if you say so, it must be the fbsplash patch for sure, I keep
    forgetting of that :-/

    >> > Could you tell if it deadlocks before init gets started or afterwards,
    >> > which fb drivers (and extra kernel patches if any) are in use.
    >> Exactly when register_framebuffer() is called, in my case, early in
    >> the boot phase, before init.
    >> >
    >> > If you have the complete backtrace of the deadlocked processes it would
    >> > help getting a better idea of what is affected and how (and why just the
    >> > framebuffer's lock is not causing trouble with earlier kernel versions).
    >> Because that code got a HUGE rewrite in the latest cycle, where
    >> registration_lock has been introduce.
    >> Just make a diff between 2.6.38 and 2.6.39. It will be easy to see
    >> that SO MANY lines have changed ;-)
    >> Anyway, since I'm out of office these days, I won't be able to send
    >> you the traceback this week, but since so many people have run into
    >> it, I guess it's fairly simple to reproduce.
    > Rewrite was not so huge, and I'm not affected here (running with KMS
    > compiled in though and vanilla kernel).
    > Probably the cause is related to one of the extra patches provided by
    > Gentoo and subscribing to framebuffer registration notifications.
    > Will have a look.

    Thanks a lot, let me know if I can help out next week.

    > Bruno

    Fabio Erculiani
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