Re: sched: memory corruption on completing completions

[Raghavendra K T]

On 02/06/2015 04:07 AM, Davidlohr Bueso wrote:
> On Thu, 2015-02-05 at 13:34 -0800, Linus Torvalds wrote:
> > On Thu, Feb 5, 2015 at 1:02 PM, Sasha Levin <sasha.levin@xxxxxxxxxx> wrote:
> > > Interestingly enough, according to that article this behaviour seems to be
> > > "by design":
> >
> > Oh, it's definitely by design, it's just that the design looked at
> > spinlocks without the admittedly very subtle issue of lifetime vs
> > unlocking.
> >
> > Spinlocks (and completions) are special - for other locks we have
> > basically allowed lifetimes to be separate from the lock state, and if
> > you have a data structure with a mutex in it, you'll have to have some
> > separate lifetime rule outside of the lock itself. But spinlocks and
> > completions have their locking state tied into their lifetime.
>
> For spinlocks I find this very much a virtue. Tight lifetimes allow the
> overall locking logic to be *simple* - keeping people from being "smart"
> and bloating up spinlocks. Similarly, I hate how the paravirt
> alternative blends in with regular (sane) bare metal code. What was
> preventing this instead??
>
> #ifdef CONFIG_PARAVIRT_SPINLOCKS
> static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
> {
> 	if (!static_key_false(&paravirt_ticketlocks_enabled))
> 		return;
>
> 	add_smp(&lock->tickets.head, TICKET_LOCK_INC);
> 	/* Do slowpath tail stuff... */
> }
> #else
> static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
> {
> 	__add(&lock->tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX);
> }
> #endif
>
> I just don't see the point to all this TICKET_SLOWPATH_FLAG:
>
> #ifdef CONFIG_PARAVIRT_SPINLOCKS
> #define __TICKET_LOCK_INC	2
> #define TICKET_SLOWPATH_FLAG	((__ticket_t)1)
> #else
> #define __TICKET_LOCK_INC	1
> #define TICKET_SLOWPATH_FLAG	((__ticket_t)0)
> #endif
>
> when it is only for paravirt -- and the word slowpath implies the
> general steps as part of the generic algorithm. Lets keep code for
> simple locks simple.

Good point, I will send this as a separate cleanup once I test the
patch I have to correct the current problem.


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/