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Re: [Xen-devel] [PATCH V3] x86 spinlock: Fix memory corruption on completing completions
- To: Oleg Nesterov <oleg@xxxxxxxxxx>
- From: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>
- Date: Thu, 12 Feb 2015 19:55:42 +0530
- Cc: jeremy@xxxxxxxx, kvm@xxxxxxxxxxxxxxx, peterz@xxxxxxxxxxxxx, jasowang@xxxxxxxxxx, virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx, paul.gortmaker@xxxxxxxxxxxxx, hpa@xxxxxxxxx, ak@xxxxxxxxxxxxxxx, a.ryabinin@xxxxxxxxxxx, x86@xxxxxxxxxx, borntraeger@xxxxxxxxxx, mingo@xxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, paulmck@xxxxxxxxxxxxxxxxxx, dave@xxxxxxxxxxxx, sasha.levin@xxxxxxxxxx, davej@xxxxxxxxxx, tglx@xxxxxxxxxxxxx, waiman.long@xxxxxx, linux-kernel@xxxxxxxxxxxxxxx, pbonzini@xxxxxxxxxx, akpm@xxxxxxxxxxxxxxxxxxxx, torvalds@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 12 Feb 2015 14:24:51 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On 02/12/2015 07:32 PM, Oleg Nesterov wrote:
Damn, sorry for noise, forgot to mention...
On 02/12, Raghavendra K T wrote:
+static inline void __ticket_check_and_clear_slowpath(arch_spinlock_t *lock,
+ __ticket_t head)
+{
+ if (head & TICKET_SLOWPATH_FLAG) {
+ arch_spinlock_t old, new;
+
+ old.tickets.head = head;
+ new.tickets.head = head & ~TICKET_SLOWPATH_FLAG;
+ old.tickets.tail = new.tickets.head + TICKET_LOCK_INC;
+ new.tickets.tail = old.tickets.tail;
+
+ /* try to clear slowpath flag when there are no contenders */
+ cmpxchg(&lock->head_tail, old.head_tail, new.head_tail);
+ }
+}
...
+clear_slowpath:
+ if (TICKET_SLOWPATH_FLAG)
+ __ticket_check_and_clear_slowpath(lock, inc.head);
I think you can remove this "if (TICKET_SLOWPATH_FLAG)" check. If it is
defined as zero, gcc should optimize out the code under "if (head & 0)".
right, the above if ( ) is unnecesary, though we would have same code
at the end, getting rid of that makes code more clean.
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