On Saturday 31 October 2015 06:45 PM, Noam Camus wrote:
> From: Noam Camus <[email protected]>
>
> If we hold rw->lock_mutex and interrupt occures we may
> end up spinning on it for ever during softirq.
>
> Below you may see an example for interrupt we get while
> nl_table_lock is holding its rw->lock_mutex and we spinned
> on it for ever.
>
> The concept for the fix was taken from SPARC.
>
> [2015-05-12 19:16:12] Stack Trace:
> [2015-05-12 19:16:12] arc_unwind_core+0xb8/0x11c
> [2015-05-12 19:16:12] dump_stack+0x68/0xac
> [2015-05-12 19:16:12] _raw_read_lock+0xa8/0xac
> [2015-05-12 19:16:12] netlink_broadcast_filtered+0x56/0x35c
> [2015-05-12 19:16:12] nlmsg_notify+0x42/0xa4
> [2015-05-12 19:16:13] neigh_update+0x1fe/0x44c
> [2015-05-12 19:16:13] neigh_event_ns+0x40/0xa4
> [2015-05-12 19:16:13] arp_process+0x46e/0x5a8
> [2015-05-12 19:16:13] __netif_receive_skb_core+0x358/0x500
> [2015-05-12 19:16:13] process_backlog+0x92/0x154
> [2015-05-12 19:16:13] net_rx_action+0xb8/0x188
> [2015-05-12 19:16:13] __do_softirq+0xda/0x1d8
> [2015-05-12 19:16:14] irq_exit+0x8a/0x8c
> [2015-05-12 19:16:14] arch_do_IRQ+0x6c/0xa8
> [2015-05-12 19:16:14] handle_interrupt_level1+0xe4/0xf0
>
> Signed-off-by: Noam Camus <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> ---
> arch/arc/include/asm/spinlock.h | 14 ++++++++++++++
> 1 files changed, 14 insertions(+), 0 deletions(-)
>
> diff --git a/arch/arc/include/asm/spinlock.h b/arch/arc/include/asm/spinlock.h
> index db8c59d..800e7c4 100644
> --- a/arch/arc/include/asm/spinlock.h
> +++ b/arch/arc/include/asm/spinlock.h
> @@ -610,7 +610,9 @@ static inline void arch_spin_unlock(arch_spinlock_t *lock)
> static inline int arch_read_trylock(arch_rwlock_t *rw)
> {
> int ret = 0;
> + unsigned long flags;
>
> + local_irq_save(flags);
> arch_spin_lock(&(rw->lock_mutex));
>
> /*
> @@ -623,6 +625,7 @@ static inline int arch_read_trylock(arch_rwlock_t *rw)
> }
>
> arch_spin_unlock(&(rw->lock_mutex));
> + local_irq_restore(flags);
>
> smp_mb();
> return ret;
> @@ -632,7 +635,9 @@ static inline int arch_read_trylock(arch_rwlock_t *rw)
> static inline int arch_write_trylock(arch_rwlock_t *rw)
> {
> int ret = 0;
> + unsigned long flags;
>
> + local_irq_save(flags);
> arch_spin_lock(&(rw->lock_mutex));
>
> /*
> @@ -646,6 +651,7 @@ static inline int arch_write_trylock(arch_rwlock_t *rw)
> ret = 1;
> }
> arch_spin_unlock(&(rw->lock_mutex));
> + local_irq_restore(flags);
>
> return ret;
> }
> @@ -664,16 +670,24 @@ static inline void arch_write_lock(arch_rwlock_t *rw)
>
> static inline void arch_read_unlock(arch_rwlock_t *rw)
> {
> + unsigned long flags;
> +
> + local_irq_save(flags);
> arch_spin_lock(&(rw->lock_mutex));
Isn't raw_spin_lock_irqsave() equivalent and more concise ?
> rw->counter++;
> arch_spin_unlock(&(rw->lock_mutex));
> + local_irq_restore(flags);
> }
>
> static inline void arch_write_unlock(arch_rwlock_t *rw)
> {
> + unsigned long flags;
> +
> + local_irq_save(flags);
> arch_spin_lock(&(rw->lock_mutex));
> rw->counter = __ARCH_RW_LOCK_UNLOCKED__;
> arch_spin_unlock(&(rw->lock_mutex));
> + local_irq_restore(flags);
> }
>
> #endif
>
On Mon, Nov 02, 2015 at 03:12:49PM +0530, Vineet Gupta wrote:
> > @@ -664,16 +670,24 @@ static inline void arch_write_lock(arch_rwlock_t *rw)
> >
> > static inline void arch_read_unlock(arch_rwlock_t *rw)
> > {
> > + unsigned long flags;
> > +
> > + local_irq_save(flags);
> > arch_spin_lock(&(rw->lock_mutex));
>
>
> Isn't raw_spin_lock_irqsave() equivalent and more concise ?
You might run into header file recursion issues; also raw_spinlock has
lockdep annotations added, whereas the above does not.