| Message ID | 20201104081549.3712-2-jgross@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | xen/locking: fix and enhance lock debugging | expand |
Hi Juergen, On 04/11/2020 08:15, Juergen Gross wrote: > Even if a spinlock was taken with interrupts on before calling > spin_trylock() with interrupts off is fine, as it can't block. > > Add a bool parameter "try" to check_lock() for handling this case. > > Remove the call of check_lock() from _spin_is_locked(), as it really > serves no purpose and it can even lead to false crashes, e.g. when > a lock was taken correctly with interrupts enabled and the call of > _spin_is_locked() happened with interrupts off. In case the lock is > taken with wrong interrupt flags this will be catched when taking > the lock. > > Signed-off-by: Juergen Gross <jgross@suse.com> > Reviewed-by: Jan Beulich <jbeulich@suse.com> Acked-by: Julien Grall <jgrall@amazon.com> Cheers, > --- > V2: > - corrected comment (Jan Beulich) > --- > xen/common/spinlock.c | 18 +++++++++++------- > 1 file changed, 11 insertions(+), 7 deletions(-) > > diff --git a/xen/common/spinlock.c b/xen/common/spinlock.c > index ce3106e2d3..b4aaf6bce6 100644 > --- a/xen/common/spinlock.c > +++ b/xen/common/spinlock.c > @@ -13,7 +13,7 @@ > > static atomic_t spin_debug __read_mostly = ATOMIC_INIT(0); > > -static void check_lock(union lock_debug *debug) > +static void check_lock(union lock_debug *debug, bool try) > { > bool irq_safe = !local_irq_is_enabled(); > > @@ -42,7 +42,13 @@ static void check_lock(union lock_debug *debug) > * > * To guard against this subtle bug we latch the IRQ safety of every > * spinlock in the system, on first use. > + * > + * A spin_trylock() with interrupts off is always fine, as this can't > + * block and above deadlock scenario doesn't apply. > */ > + if ( try && irq_safe ) > + return; > + > if ( unlikely(debug->irq_safe != irq_safe) ) > { > union lock_debug seen, new = { 0 }; > @@ -102,7 +108,7 @@ void spin_debug_disable(void) > > #else /* CONFIG_DEBUG_LOCKS */ > > -#define check_lock(l) ((void)0) > +#define check_lock(l, t) ((void)0) > #define check_barrier(l) ((void)0) > #define got_lock(l) ((void)0) > #define rel_lock(l) ((void)0) > @@ -159,7 +165,7 @@ void inline _spin_lock_cb(spinlock_t *lock, void (*cb)(void *), void *data) > spinlock_tickets_t tickets = SPINLOCK_TICKET_INC; > LOCK_PROFILE_VAR; > > - check_lock(&lock->debug); > + check_lock(&lock->debug, false); > preempt_disable(); > tickets.head_tail = arch_fetch_and_add(&lock->tickets.head_tail, > tickets.head_tail); > @@ -220,8 +226,6 @@ void _spin_unlock_irqrestore(spinlock_t *lock, unsigned long flags) > > int _spin_is_locked(spinlock_t *lock) > { > - check_lock(&lock->debug); > - > /* > * Recursive locks may be locked by another CPU, yet we return > * "false" here, making this function suitable only for use in > @@ -236,7 +240,7 @@ int _spin_trylock(spinlock_t *lock) > { > spinlock_tickets_t old, new; > > - check_lock(&lock->debug); > + check_lock(&lock->debug, true); > old = observe_lock(&lock->tickets); > if ( old.head != old.tail ) > return 0; > @@ -294,7 +298,7 @@ int _spin_trylock_recursive(spinlock_t *lock) > BUILD_BUG_ON(NR_CPUS > SPINLOCK_NO_CPU); > BUILD_BUG_ON(SPINLOCK_RECURSE_BITS < 3); > > - check_lock(&lock->debug); > + check_lock(&lock->debug, true); > > if ( likely(lock->recurse_cpu != cpu) ) > { >
diff --git a/xen/common/spinlock.c b/xen/common/spinlock.c index ce3106e2d3..b4aaf6bce6 100644 --- a/xen/common/spinlock.c +++ b/xen/common/spinlock.c @@ -13,7 +13,7 @@ static atomic_t spin_debug __read_mostly = ATOMIC_INIT(0); -static void check_lock(union lock_debug *debug) +static void check_lock(union lock_debug *debug, bool try) { bool irq_safe = !local_irq_is_enabled(); @@ -42,7 +42,13 @@ static void check_lock(union lock_debug *debug) * * To guard against this subtle bug we latch the IRQ safety of every * spinlock in the system, on first use. + * + * A spin_trylock() with interrupts off is always fine, as this can't + * block and above deadlock scenario doesn't apply. */ + if ( try && irq_safe ) + return; + if ( unlikely(debug->irq_safe != irq_safe) ) { union lock_debug seen, new = { 0 }; @@ -102,7 +108,7 @@ void spin_debug_disable(void) #else /* CONFIG_DEBUG_LOCKS */ -#define check_lock(l) ((void)0) +#define check_lock(l, t) ((void)0) #define check_barrier(l) ((void)0) #define got_lock(l) ((void)0) #define rel_lock(l) ((void)0) @@ -159,7 +165,7 @@ void inline _spin_lock_cb(spinlock_t *lock, void (*cb)(void *), void *data) spinlock_tickets_t tickets = SPINLOCK_TICKET_INC; LOCK_PROFILE_VAR; - check_lock(&lock->debug); + check_lock(&lock->debug, false); preempt_disable(); tickets.head_tail = arch_fetch_and_add(&lock->tickets.head_tail, tickets.head_tail); @@ -220,8 +226,6 @@ void _spin_unlock_irqrestore(spinlock_t *lock, unsigned long flags) int _spin_is_locked(spinlock_t *lock) { - check_lock(&lock->debug); - /* * Recursive locks may be locked by another CPU, yet we return * "false" here, making this function suitable only for use in @@ -236,7 +240,7 @@ int _spin_trylock(spinlock_t *lock) { spinlock_tickets_t old, new; - check_lock(&lock->debug); + check_lock(&lock->debug, true); old = observe_lock(&lock->tickets); if ( old.head != old.tail ) return 0; @@ -294,7 +298,7 @@ int _spin_trylock_recursive(spinlock_t *lock) BUILD_BUG_ON(NR_CPUS > SPINLOCK_NO_CPU); BUILD_BUG_ON(SPINLOCK_RECURSE_BITS < 3); - check_lock(&lock->debug); + check_lock(&lock->debug, true); if ( likely(lock->recurse_cpu != cpu) ) {