[PARISC] Enable interrupts while spinning
Use the __raw_spin_lock_flags routine so we can take an interrupt while
spinning. This re-fixes a bug jejb found on 2005-10-20:
CPU0 does a flush_tlb_all holding the vmlist_lock for write.
CPU1 tries a cat of /proc/meminfo which tries to acquire vmlist_lock for read
CPU1 is now spinning with interrupts disabled
CPU0 tries to execute a smp_call_function to flush the local tlb caches
This is now a deadlock because CPU1 is spinning with interrupts disabled and
can never receive the IPI
Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>
diff --git a/include/asm-parisc/spinlock.h b/include/asm-parisc/spinlock.h
index 8980a87..f3d2090 100644
--- a/include/asm-parisc/spinlock.h
+++ b/include/asm-parisc/spinlock.h
@@ -57,35 +57,42 @@
/*
* Read-write spinlocks, allowing multiple readers but only one writer.
- * The spinlock is held by the writer, preventing any readers or other
- * writers from grabbing the rwlock. Readers use the lock to serialise their
- * access to the counter (which records how many readers currently hold the
- * lock). Linux rwlocks are unfair to writers; they can be starved for
- * an indefinite time by readers. They can also be taken in interrupt context,
- * so we have to disable interrupts when acquiring the spin lock to be sure
- * that an interrupting reader doesn't get an inconsistent view of the lock.
+ * Linux rwlocks are unfair to writers; they can be starved for an indefinite
+ * time by readers. With care, they can also be taken in interrupt context.
+ *
+ * In the PA-RISC implementation, we have a spinlock and a counter.
+ * Readers use the lock to serialise their access to the counter (which
+ * records how many readers currently hold the lock).
+ * Writers hold the spinlock, preventing any readers or other writers from
+ * grabbing the rwlock.
*/
+/* Note that we have to ensure interrupts are disabled in case we're
+ * interrupted by some other code that wants to grab the same read lock */
static __inline__ void __raw_read_lock(raw_rwlock_t *rw)
{
unsigned long flags;
local_irq_save(flags);
- __raw_spin_lock(&rw->lock);
+ __raw_spin_lock_flags(&rw->lock, flags);
rw->counter++;
__raw_spin_unlock(&rw->lock);
local_irq_restore(flags);
}
+/* Note that we have to ensure interrupts are disabled in case we're
+ * interrupted by some other code that wants to grab the same read lock */
static __inline__ void __raw_read_unlock(raw_rwlock_t *rw)
{
unsigned long flags;
local_irq_save(flags);
- __raw_spin_lock(&rw->lock);
+ __raw_spin_lock_flags(&rw->lock, flags);
rw->counter--;
__raw_spin_unlock(&rw->lock);
local_irq_restore(flags);
}
+/* Note that we have to ensure interrupts are disabled in case we're
+ * interrupted by some other code that wants to grab the same read lock */
static __inline__ int __raw_read_trylock(raw_rwlock_t *rw)
{
unsigned long flags;
@@ -110,12 +117,14 @@
goto retry;
}
+/* Note that we have to ensure interrupts are disabled in case we're
+ * interrupted by some other code that wants to read_trylock() this lock */
static __inline__ void __raw_write_lock(raw_rwlock_t *rw)
{
unsigned long flags;
retry:
local_irq_save(flags);
- __raw_spin_lock(&rw->lock);
+ __raw_spin_lock_flags(&rw->lock, flags);
if (rw->counter != 0) {
__raw_spin_unlock(&rw->lock);
@@ -138,6 +147,8 @@
__raw_spin_unlock(&rw->lock);
}
+/* Note that we have to ensure interrupts are disabled in case we're
+ * interrupted by some other code that wants to read_trylock() this lock */
static __inline__ int __raw_write_trylock(raw_rwlock_t *rw)
{
unsigned long flags;