Messages in this thread | | | Date | Tue, 27 Apr 2010 11:25:30 +0200 | From | Ingo Molnar <> | Subject | Re: [GIT PULL v2] Preparation for BKL'ed ioctl removal |
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* Arnd Bergmann <arnd@arndb.de> wrote:
> On Monday 26 April 2010, Ingo Molnar wrote: > > This could be done all automated for a hundred old drivers if need to be. > > There would be no bkl_ioctl's left. > > I don't think it can be fully automated. [...]
Corner cases are not a problem as long as the risk of them going unnoticed is lower than the risk of a manual conversion introducing bugs.
> [...] For the majority of the modules, your approach would work fine, but > there are still the well-known pitfalls in corner cases: > > - recursive uses in functions outside of ioctl (possibly none left > after the TTY layer is done, but who knows)
Not a problem even if there's any such usage left: lockdep will sort those out very quickly.
> - lock-order problems with other mutexes (see DRM)
This too will be mapped out very quickly via lockdep.
> - code that depends on autorelease to allow one ioctl while another > is sleeping. (a small number of drivers)
This is a real issue, and in fact it's an unknown: there may be an unknown number of random sleep points within BKL codepaths that is being relied on in creative ways.
Note that by introducing a mutex we (in most cases) make the locking _stricter_, so the biggest risk from that is a lockup - which will be debuggable via lockdep.
Ingo
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