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  1. 25 Feb, 2008 2 commits
  3. 23 Feb, 2008 2 commits
    • Linus Torvalds's avatar
      Add memory barrier semantics to wake_up() & co · 04e2f174
      Linus Torvalds authored 
      
Oleg Nesterov and others have pointed out that on some architectures,
the traditional sequence of

	set_current_state(TASK_INTERRUPTIBLE);
	if (CONDITION)
		return;
	schedule();

is racy wrt another CPU doing

	CONDITION = 1;
	wake_up_process(p);

because while set_current_state() has a memory barrier separating
setting of the TASK_INTERRUPTIBLE state from reading of the CONDITION
variable, there is no such memory barrier on the wakeup side.

Now, wake_up_process() does actually take a spinlock before it reads and
sets the task state on the waking side, and on x86 (and many other
architectures) that spinlock is in fact equivalent to a memory barrier,
but that is not generally guaranteed.  The write that sets CONDITION
could move into the critical region protected by the runqueue spinlock.

However, adding a smp_wmb() to before the spinlock should now order the
writing of CONDITION wrt the lock itself, which in turn is ordered wrt
the accesses within the spinlock (which includes the reading of the old
state).

This should thus close the race (which probably has never been seen in
practice, but since smp_wmb() is a no-op on x86, it's not like this will
make anything worse either on the most common architecture where the
spinlock already gave the required protection).
Acked-by: default avatarOleg Nesterov <oleg@tv-sign.ru>
Acked-by: default avatarDmitry Adamushko <dmitry.adamushko@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      04e2f174
    • Srinivasa Ds's avatar
      kprobes: refuse kprobe insertion on add/sub_preempt_counter() · 43627582
      Srinivasa Ds authored 
      
Kprobes makes use of preempt_disable(),preempt_enable_noresched() and these
functions inturn call add/sub_preempt_count().  So we need to refuse user from
inserting probe in to these functions.

This patch disallows user from probing add/sub_preempt_count().
Signed-off-by: default avatarSrinivasa DS <srinivasa@in.ibm.com>
Acked-by: default avatarAnanth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      43627582
  5. 13 Feb, 2008 7 commits
  7. 08 Feb, 2008 1 commit
  9. 31 Jan, 2008 1 commit
  11. 30 Jan, 2008 1 commit
    • Nick Piggin's avatar
      spinlock: lockbreak cleanup · 95c354fe
      Nick Piggin authored 
      
The break_lock data structure and code for spinlocks is quite nasty.
Not only does it double the size of a spinlock but it changes locking to
a potentially less optimal trylock.

Put all of that under CONFIG_GENERIC_LOCKBREAK, and introduce a
__raw_spin_is_contended that uses the lock data itself to determine whether
there are waiters on the lock, to be used if CONFIG_GENERIC_LOCKBREAK is
not set.

Rename need_lockbreak to spin_needbreak, make it use spin_is_contended to
decouple it from the spinlock implementation, and make it typesafe (rwlocks
do not have any need_lockbreak sites -- why do they even get bloated up
with that break_lock then?).
Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      95c354fe
  13. 25 Jan, 2008 26 commits

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