| Date | Thu, 21 Oct 2004 13:11:17 +0200 | From | Jens Axboe <> | Subject | Re: [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U8 |
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On Thu, Oct 21 2004, Thomas Gleixner wrote: > 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.
Semaphore and mutex has always been the same thing in Linux. Apparently this isn't so in Ingos tree, you should make a clear distinction on which you are discussing.
-- Jens Axboe
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