Date: Thu, 7 Aug 2008 10:16:42 -0400 From: John Baldwin <jhb@freebsd.org> To: Hans Petter Selasky <hselasky@freebsd.org> Cc: Perforce Change Reviews <perforce@freebsd.org> Subject: Re: PERFORCE change 144415 for review Message-ID: <200808071016.43108.jhb@freebsd.org> In-Reply-To: <200807011103.m61B3x2b079270@repoman.freebsd.org> References: <200807011103.m61B3x2b079270@repoman.freebsd.org>
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On Tuesday 01 July 2008 07:03:59 am Hans Petter Selasky wrote: > http://perforce.freebsd.org/chv.cgi?CH=144415 > > Change 144415 by hselasky@hselasky_laptop001 on 2008/07/01 11:03:31 > > > To allow USB drivers using the Giant mutex, like ukbd > and the tty layer (ucom), condition variable functions > like mtx_sleep() and cv_wait() needs to support the Giant > mutex. Previously using the Giant mutex with these functions > resulted in a panic due to an unlock race between the > GIANT_DROP macro and the internal mutex unlock in the > condition variable function. This patch will try to > resolve that race. I'd rather that the sleep and condition variable code just explicitly handle this case rather than changing DROP_GIANT(). > Affected files ... > > .. //depot/projects/usb/src/sys/kern/kern_condvar.c#7 edit > .. //depot/projects/usb/src/sys/kern/kern_synch.c#9 edit > .. //depot/projects/usb/src/sys/sys/mutex.h#8 edit > > Differences ... > > ==== //depot/projects/usb/src/sys/kern/kern_condvar.c#7 (text+ko) ==== > > @@ -123,7 +123,7 @@ > sleepq_lock(cvp); > > cvp->cv_waiters++; > - DROP_GIANT(); > + DROP_GIANT(lock); > > sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0); > if (class->lc_flags & LC_SLEEPABLE) > @@ -176,7 +176,7 @@ > sleepq_lock(cvp); > > cvp->cv_waiters++; > - DROP_GIANT(); > + DROP_GIANT(lock); > > sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0); > if (class->lc_flags & LC_SLEEPABLE) > @@ -233,7 +233,7 @@ > sleepq_lock(cvp); > > cvp->cv_waiters++; > - DROP_GIANT(); > + DROP_GIANT(lock); > > sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR | > SLEEPQ_INTERRUPTIBLE, 0); > @@ -293,7 +293,7 @@ > sleepq_lock(cvp); > > cvp->cv_waiters++; > - DROP_GIANT(); > + DROP_GIANT(lock); > > sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0); > sleepq_set_timeout(cvp, timo); > @@ -356,7 +356,7 @@ > sleepq_lock(cvp); > > cvp->cv_waiters++; > - DROP_GIANT(); > + DROP_GIANT(lock); > > sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR | > SLEEPQ_INTERRUPTIBLE, 0); > > ==== //depot/projects/usb/src/sys/kern/kern_synch.c#9 (text+ko) ==== > > @@ -181,7 +181,7 @@ > CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)", > td->td_tid, p->p_pid, td->td_name, wmesg, ident); > > - DROP_GIANT(); > + DROP_GIANT(lock); > if (lock != NULL && !(class->lc_flags & LC_SLEEPABLE)) { > WITNESS_SAVE(lock, lock_witness); > lock_state = class->lc_unlock(lock); > > ==== //depot/projects/usb/src/sys/sys/mutex.h#8 (text+ko) ==== > > @@ -366,17 +366,44 @@ > * > * Note that DROP_GIANT*() needs to be paired with PICKUP_GIANT() > * The #ifndef is to allow lint-like tools to redefine DROP_GIANT. > + * > + * Note that by default DROP_GIANT takes no argument. Optionally you > + * can specify an argument which explicitly has the name "lock" and > + * type "struct lock_object *". If this "lock" pointer is equal to > + * "&Giant", the DROP_GIANT macro will not do the final drop on the > + * Giant mutex, but expects the calling code to do so. This feature is > + * used by condition variables to allow sleeping on Giant. The > + * condition variable code will then do the final drop! > */ > #ifndef DROP_GIANT > -#define DROP_GIANT() \ > +#define DROP_GIANT(arg) DROP_GIANT_SUB_##arg(arg) > +#define DROP_GIANT_SUB_lock(arg) DROP_GIANT_SUB(arg) /* "lock" argument */ > +#define DROP_GIANT_SUB_(arg) DROP_GIANT_SUB(NULL) /* no argument */ > +#define DROP_GIANT_SUB(lock) \ > do { \ > - int _giantcnt = 0; \ > + unsigned int _giantcnt; \ > WITNESS_SAVE_DECL(Giant); \ > \ > if (mtx_owned(&Giant)) { \ > - WITNESS_SAVE(&Giant.lock_object, Giant); \ > - for (_giantcnt = 0; mtx_owned(&Giant); _giantcnt++) \ > - mtx_unlock(&Giant); \ > + unsigned int _giantn; \ > + if (((void *)(lock)) == ((void *)&Giant)) { \ > + /* special case */ \ > + _giantn = Giant.mtx_recurse; \ > + } else { \ > + /* default case */ \ > + _giantn = Giant.mtx_recurse + 1; \ > + } \ > + if (_giantn != 0) { \ > + WITNESS_SAVE(&Giant.lock_object, Giant); \ > + _giantcnt = _giantn; \ > + do { \ > + mtx_unlock(&Giant); \ > + } while (--_giantn); \ > + } else { \ > + _giantcnt = 0; \ > + } \ > + } else { \ > + _giantcnt = 0; \ > } > > #define PICKUP_GIANT() \ > -- John Baldwin
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