Messages in this thread | | | Date | Mon, 23 Jun 2008 21:22:03 +0200 | From | Marcin Slusarz <> | Subject | Re: [PATCH] Fix open/close race in saa7134 |
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On Mon, Jun 23, 2008 at 11:54:32AM -0700, Arjan van de Ven wrote: > On Mon, 23 Jun 2008 20:49:42 +0200 > Marcin Slusarz <marcin.slusarz@gmail.com> wrote: > > > On Sun, Jun 22, 2008 at 10:58:32AM -0700, Arjan van de Ven wrote: > > > On Sun, 22 Jun 2008 19:33:37 +0200 > > > Marcin Slusarz <marcin.slusarz@gmail.com> wrote: > > > > > > > On Sun, Jun 22, 2008 at 10:05:07AM -0700, Arjan van de Ven wrote: > > > > > > > > > > From: Arjan van de Ven <arjan@linux.intel.com> > > > > > Date: Sun, 22 Jun 2008 10:03:02 -0700 > > > > > Subject: [PATCH] Fix open/close race in saa7134 > > > > > > > > > > The saa7134 driver uses a (non-atomic) variable in an attempt to > > > > > only allow one opener of the device (how it deals with sending > > > > > the fd over unix sockets I don't know). > > > > > > > > > > Unfortunately, the release function first decrements this > > > > > variable, and THEN goes on to disable more of the device. This > > > > > allows for a race where another opener of the device comes in > > > > > after the decrement of the variable, configures the hardware > > > > > just to then see the hardware be disabled by the rest of the > > > > > release function. > > > > > > > > Simplier fix: > > > > http://lkml.org/lkml/2008/6/9/308 > > > > But I don't remember whether it was applied or not... > > > > > > > > > the patch might be simpler, but it's not fully correct... > > > the decrement is non-atomic and not protected by any lock > > > whatsoever. > > > > It's not atomic, but it don't have to, because there's only one > > thread which "owns" the device. > > this is not correct! > > this is a close->open race, not an open->close! > which means the guy who's closing it and the guy who's then opening it > again do not have to be the same guy
If dev->empress_users could be > 1 then ok - it could break, but it can only be 1 or 0. If it's 1 you won't open the device. If it's 0 you won't reach ts_close.
If you still see the race, please show me the sequence, because I don't (of course when decrementing is the last operation of ts_close).
Marcin
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