Date: Tue, 1 Jul 2008 11:03:59 GMT From: Hans Petter Selasky <hselasky@FreeBSD.org> To: Perforce Change Reviews <perforce@FreeBSD.org> Subject: PERFORCE change 144415 for review Message-ID: <200807011103.m61B3x2b079270@repoman.freebsd.org>
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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. 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() \
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