[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 4/4] xen/rcu: add assertions to debug build
On Tue, Feb 18, 2020 at 01:21:14PM +0100, Juergen Gross wrote: > Xen's RCU implementation relies on no softirq handling taking place > while being in a RCU critical section. Add ASSERT()s in debug builds > in order to catch any violations. > > For that purpose modify rcu_read_[un]lock() to use a dedicated percpu > counter instead of preempt_[en|dis]able() as this enables to test > that condition in __do_softirq() (ASSERT_NOT_IN_ATOMIC() is not > usable there due to __cpu_up() calling process_pending_softirqs() > while holding the cpu hotplug lock). > > Dropping the now no longer needed #include of preempt.h in rcupdate.h > requires adding it in some sources. > > Signed-off-by: Juergen Gross <jgross@xxxxxxxx> > --- > xen/common/multicall.c | 1 + > xen/common/rcupdate.c | 4 ++++ > xen/common/softirq.c | 2 ++ > xen/common/wait.c | 1 + > xen/include/xen/rcupdate.h | 21 +++++++++++++++++---- > 5 files changed, 25 insertions(+), 4 deletions(-) > > diff --git a/xen/common/multicall.c b/xen/common/multicall.c > index 5a199ebf8f..67f1a23485 100644 > --- a/xen/common/multicall.c > +++ b/xen/common/multicall.c > @@ -10,6 +10,7 @@ > #include <xen/multicall.h> > #include <xen/guest_access.h> > #include <xen/perfc.h> > +#include <xen/preempt.h> > #include <xen/trace.h> > #include <asm/current.h> > #include <asm/hardirq.h> > diff --git a/xen/common/rcupdate.c b/xen/common/rcupdate.c > index e6add0b120..b03f4b44d9 100644 > --- a/xen/common/rcupdate.c > +++ b/xen/common/rcupdate.c > @@ -46,6 +46,10 @@ > #include <xen/cpu.h> > #include <xen/stop_machine.h> > > +#ifndef NDEBUG > +DEFINE_PER_CPU(unsigned int, rcu_lock_cnt); > +#endif > + > /* Global control variables for rcupdate callback mechanism. */ > static struct rcu_ctrlblk { > long cur; /* Current batch number. */ > diff --git a/xen/common/softirq.c b/xen/common/softirq.c > index 3fe75ca3e8..18be8db0c6 100644 > --- a/xen/common/softirq.c > +++ b/xen/common/softirq.c > @@ -30,6 +30,8 @@ static void __do_softirq(unsigned long ignore_mask, bool > rcu_allowed) > unsigned int i, cpu; > unsigned long pending; > > + ASSERT(!rcu_allowed || rcu_quiesce_allowed()); > + > for ( ; ; ) > { > /* > diff --git a/xen/common/wait.c b/xen/common/wait.c > index 24716e7676..9cdb174036 100644 > --- a/xen/common/wait.c > +++ b/xen/common/wait.c > @@ -19,6 +19,7 @@ > * along with this program; If not, see <http://www.gnu.org/licenses/>. > */ > > +#include <xen/preempt.h> > #include <xen/sched.h> > #include <xen/softirq.h> > #include <xen/wait.h> > diff --git a/xen/include/xen/rcupdate.h b/xen/include/xen/rcupdate.h > index 87f35b7704..a5ee7fec2b 100644 > --- a/xen/include/xen/rcupdate.h > +++ b/xen/include/xen/rcupdate.h > @@ -34,10 +34,23 @@ > #include <xen/cache.h> > #include <xen/spinlock.h> > #include <xen/cpumask.h> > -#include <xen/preempt.h> > +#include <xen/percpu.h> > > #define __rcu > > +#ifndef NDEBUG > +DECLARE_PER_CPU(unsigned int, rcu_lock_cnt); > + > +#define rcu_quiesce_disable() (this_cpu(rcu_lock_cnt))++ > +#define rcu_quiesce_enable() (this_cpu(rcu_lock_cnt))-- I think you need a barrier here like it's currently used in preempt_{enabled/disable}, or use arch_lock_{acquire/release}_barrier which would be better IMO. > +#define rcu_quiesce_allowed() (!this_cpu(rcu_lock_cnt)) ASSERT_NOT_IN_ATOMIC should be expanded to also assert !this_cpu(rcu_lock_cnt), or else missing pairs of rcu_read_{lock/unlock} would be undetected. Thanks, Roger. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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