ChangeSet 1.2231.1.127, 2005/03/28 19:51:53-08:00, [EMAIL PROTECTED]
[PATCH] break_lock fix
lock->break_lock is set when a lock is contended, but cleared only in
cond_resched_lock. Users of need_lockbreak (journal_commit_transaction,
copy_pte_range, unmap_vmas) don't necessarily use cond_resched_lock on
it.
So, if the lock has been contended at some time in the past, break_lock
remains set thereafter, and the fastpath keeps dropping lock
unnecessarily.
Hanging the system if you make a change like I did, forever restarting
a
loop before making any progress. And even users of cond_resched_lock
may
well suffer an initial unnecessary lockbreak.
There seems to be no point at which break_lock can be cleared when
unlocking, any point being either too early or too late; but that's
okay,
it's only of interest while the lock is held. So clear it whenever the
lock is acquired - and any waiting contenders will quickly set it again.
Additional locking overhead? well, this is only when CONFIG_PREEMPT is
on.
Since cond_resched_lock's spin_lock clears break_lock, no need to clear
it
itself; and use need_lockbreak there too, preferring optimizer to
#ifdefs.
Signed-off-by: Hugh Dickins <[EMAIL PROTECTED]>
Signed-off-by: Ingo Molnar <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
sched.c | 5 +----
spinlock.c | 2 ++
2 files changed, 3 insertions(+), 4 deletions(-)
diff -Nru a/kernel/sched.c b/kernel/sched.c
--- a/kernel/sched.c 2005-03-28 21:34:33 -08:00
+++ b/kernel/sched.c 2005-03-28 21:34:33 -08:00
@@ -3741,14 +3741,11 @@
*/
int cond_resched_lock(spinlock_t * lock)
{
-#if defined(CONFIG_SMP) && defined(CONFIG_PREEMPT)
- if (lock->break_lock) {
- lock->break_lock = 0;
+ if (need_lockbreak(lock)) {
spin_unlock(lock);
cpu_relax();
spin_lock(lock);
}
-#endif
if (need_resched()) {
_raw_spin_unlock(lock);
preempt_enable_no_resched();
diff -Nru a/kernel/spinlock.c b/kernel/spinlock.c
--- a/kernel/spinlock.c 2005-03-28 21:34:33 -08:00
+++ b/kernel/spinlock.c 2005-03-28 21:34:33 -08:00
@@ -187,6 +187,7 @@
cpu_relax(); \
preempt_disable(); \
} \
+ (lock)->break_lock = 0; \
} \
\
EXPORT_SYMBOL(_##op##_lock); \
@@ -209,6 +210,7 @@
cpu_relax(); \
preempt_disable(); \
} \
+ (lock)->break_lock = 0; \
return flags; \
} \
\
-
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