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[IA64] remove staled comments in asm/system.h 

With the recent optimization made to wrap_mmu_context function,
we don't hold tasklist_lock anymore when wrapping context id.
The comments in asm/system.h must fall through the crack earlier.
Remove staled comments.

I believe it is still beneficial to unlock the runqueue lock
across context switch. So leave __ARCH_WANT_UNLOCKED_CTXSW on.

Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
This commit is contained in:
Chen, Kenneth W 2006-01-26 18:24:59 -08:00 committed by Tony Luck
parent df080e7c94
commit f8efa27662
1 changed files with 0 additions and 25 deletions
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25
include/asm-ia64/system.h
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@ -249,32 +249,7 @@ extern void ia64_load_extra (struct task_struct *task);
# define switch_to(prev,next,last) __switch_to(prev, next, last)
#endif
/*
* On IA-64, we don't want to hold the runqueue's lock during the low-level context-switch,
* because that could cause a deadlock. Here is an example by Erich Focht:
*
* Example:
* CPU#0:
* schedule()
* -> spin_lock_irq(&rq->lock)
* -> context_switch()
* -> wrap_mmu_context()
* -> read_lock(&tasklist_lock)
*
* CPU#1:
* sys_wait4() or release_task() or forget_original_parent()
* -> write_lock(&tasklist_lock)
* -> do_notify_parent()
* -> wake_up_parent()
* -> try_to_wake_up()
* -> spin_lock_irq(&parent_rq->lock)
*
* If the parent's rq happens to be on CPU#0, we'll wait for the rq->lock
* of that CPU which will not be released, because there we wait for the
* tasklist_lock to become available.
*/
#define __ARCH_WANT_UNLOCKED_CTXSW
#define ARCH_HAS_PREFETCH_SWITCH_STACK
#define ia64_platform_is(x) (strcmp(x, platform_name) == 0)