| Subject | Re: [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U8 | From | Thomas Gleixner <> | Date | Thu, 21 Oct 2004 12:11:45 +0200 |
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On Thu, 2004-10-21 at 12:11, Jens Axboe wrote: > On Thu, Oct 21 2004, Thomas Gleixner wrote: > > On Thu, 2004-10-21 at 11:53, Jens Axboe wrote: > > > On Thu, Oct 21 2004, Thomas Gleixner wrote: > > > > On Thu, 2004-10-21 at 11:12, Rui Nuno Capela wrote: > > > > > [<e018e139>] queuecommand+0x70/0x7c [usb_storage] (24) > > > > > > > > As I already pointed out, this is a problem due to up(sema) in > > > > queuecommand. That's one of the semaphore abuse points, which needs to > > > > be fixed. > > > > > > > > The problem is that semaphores are hold by Process A and released by > > > > Process B, which makes Ingo's checks trigger > > > > > > That's utter crap, it's perfectly valid use. > > > > It's not! > > > > >From the code: > > > > init_MUTEX_LOCKED(&(us->sema)); > > > > This is used to wait for command completion and therefor we have the > > completion API. It was used this way because the ancestor of completion > > (sleep_on) was racy ! > > I didn't look at the USB code, I'm just saying that it's perfectly valid > use of a semaphore the pattern you describe (process A holding it, > process B releasing it).
Yeah, for a semaphore it is, but not for a mutex.
IMHO, this is not clearly seperated and therefor produces a lot of confusion.
tglx
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