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Subject[PREEMPT_RT] [PATCH 1/2] Introduce write_trylock_irqsave
Date
Hi Ingo,

I am trying to fix the BUG I mentioned here:
http://lkml.org/lkml/2007/04/20/41. The problem arises because
ptrace_attach() calls local_irq_disable() and write_trylock() and later calls
write_unlock_irq. On -rt write_unlock_irq doesn't restore irqs for regular
rwlock_t, so irqs remain disabled. I have also sent patches for mainline
kernel. Please refer http://lkml.org/lkml/2007/05/09/76 ,
http://lkml.org/lkml/2007/05/09/79 and http://lkml.org/lkml/2007/05/09/550

This patch adds write_trylock_irqsave function.

Signed-off-by: Sripathi Kodi <sripathik@in.ibm.com>

Index: linux-2.6.21-rt1_patch/include/linux/spinlock.h
===================================================================
--- linux-2.6.21-rt1_patch.orig/include/linux/spinlock.h 2007-05-10
11:28:35.000000000 +0530
+++ linux-2.6.21-rt1_patch/include/linux/spinlock.h 2007-05-10
11:29:13.000000000 +0530
@@ -323,6 +323,7 @@

# define _read_trylock(rwl) rt_read_trylock(rwl)
# define _write_trylock(rwl) rt_write_trylock(rwl)
+#define _write_trylock_irqsave(rwl, flags) rt_write_trylock_irqsave(rwl,
flags)

# define _read_lock(rwl) rt_read_lock(rwl)
# define _write_lock(rwl) rt_write_lock(rwl)
@@ -398,6 +399,19 @@
else __bad_rwlock_type(); \
} while (0)

+#define PICK_RW_OP2_RET(optype, op, lock, flags) \
+({ \
+ unsigned long __ret; \
+ \
+ if (TYPE_EQUAL((lock), raw_rwlock_t)) \
+ __ret = __##optype##op((raw_rwlock_t *)(lock), flags); \
+ else if (TYPE_EQUAL(lock, rwlock_t)) \
+ __ret = _##optype##op((rwlock_t *)(lock), flags); \
+ else __bad_rwlock_type(); \
+ \
+ __ret; \
+})
+
#ifdef CONFIG_DEBUG_SPINLOCK
extern void __raw_spin_lock_init(raw_spinlock_t *lock, const char *name,
struct lock_class_key *key);
@@ -473,6 +487,9 @@
//#define write_trylock(lock) _write_trylock(lock)
#define write_trylock(lock) __cond_lock(lock, PICK_RW_OP_RET(write, _trylock,
lock))

+#define write_trylock_irqsave(lock, flags) \
+ __cond_lock(lock, PICK_RW_OP2_RET(write, _trylock_irqsave, lock, &flags))
+
#define __spin_can_lock(lock) __raw_spin_can_lock(&(lock)->raw_lock)
#define __read_can_lock(lock) __raw_read_can_lock(&(lock)->raw_lock)
#define __write_can_lock(lock) __raw_write_can_lock(&(lock)->raw_lock)
Index: linux-2.6.21-rt1_patch/include/linux/spinlock_api_smp.h
===================================================================
--- linux-2.6.21-rt1_patch.orig/include/linux/spinlock_api_smp.h 2007-05-10
11:28:35.000000000 +0530
+++ linux-2.6.21-rt1_patch/include/linux/spinlock_api_smp.h 2007-05-10
11:29:13.000000000 +0530
@@ -48,6 +48,8 @@
__spin_trylock_irqsave(raw_spinlock_t *lock, unsigned long *flags);
int __lockfunc __read_trylock(raw_rwlock_t *lock);
int __lockfunc __write_trylock(raw_rwlock_t *lock);
+int __lockfunc
+__write_trylock_irqsave(raw_rwlock_t *lock, unsigned long *flags);
int __lockfunc __spin_trylock_bh(raw_spinlock_t *lock);
int __lockfunc __spin_trylock_irq(raw_spinlock_t *lock);
void __lockfunc __spin_unlock(raw_spinlock_t *lock) RELEASE_SPIN;
Index: linux-2.6.21-rt1_patch/include/linux/spinlock_api_up.h
===================================================================
--- linux-2.6.21-rt1_patch.orig/include/linux/spinlock_api_up.h 2007-05-10
11:28:35.000000000 +0530
+++ linux-2.6.21-rt1_patch/include/linux/spinlock_api_up.h 2007-05-10
11:29:13.000000000 +0530
@@ -41,6 +41,8 @@

#define __spin_trylock_irqsave(lock, flags) __TRYLOCK_IRQSAVE(lock, flags)

+#define __write_trylock_irqsave(lock, flags) __TRYLOCK_IRQSAVE(lock, flags)
+
#define __UNLOCK(lock) \
do { preempt_enable(); __release(lock); (void)(lock); } while (0)

Index: linux-2.6.21-rt1_patch/kernel/rt.c
===================================================================
--- linux-2.6.21-rt1_patch.orig/kernel/rt.c 2007-05-10 11:28:35.000000000
+0530
+++ linux-2.6.21-rt1_patch/kernel/rt.c 2007-05-10 11:29:13.000000000 +0530
@@ -173,6 +173,12 @@
}
EXPORT_SYMBOL(rt_write_trylock);

+int __lockfunc rt_write_trylock_irqsave(rwlock_t *rwlock, unsigned long
*flags)
+{
+ *flags = 0;
+ return rt_write_trylock(rwlock);
+}
+
int __lockfunc rt_read_trylock(rwlock_t *rwlock)
{
struct rt_mutex *lock = &rwlock->lock;
Index: linux-2.6.21-rt1_patch/kernel/spinlock.c
===================================================================
--- linux-2.6.21-rt1_patch.orig/kernel/spinlock.c 2007-05-10
11:28:35.000000000 +0530
+++ linux-2.6.21-rt1_patch/kernel/spinlock.c 2007-05-10 11:29:13.000000000
+0530
@@ -97,6 +97,20 @@
}
EXPORT_SYMBOL(__write_trylock);

+int __lockfunc __write_trylock_irqsave(raw_rwlock_t *lock, unsigned long
*flags)
+{
+ int ret;
+
+ local_irq_save(*flags);
+ ret = __write_trylock(lock);
+ if (ret)
+ return ret;
+
+ local_irq_restore(*flags);
+ return 0;
+}
+EXPORT_SYMBOL(__write_trylock_irqsave);
+
/*
* If lockdep is enabled then we use the non-preemption spin-ops
* even on CONFIG_PREEMPT, because lockdep assumes that interrupts are
-
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