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Date: Tue, 19 Sep 2023 14:57:52 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
Alexey Dobriyan <adobriyan@...il.com>,
linux-kernel@...r.kernel.org,
Linus Walleij <linus.walleij@...aro.org>,
akpm@...ux-foundation.org
Subject: Re: Buggy __free(kfree) usage pattern already in tree
On Sat, Sep 16, 2023 at 12:13:32AM +0200, Peter Zijlstra wrote:
> I think I can make it work, I'll go have a play, but perhaps not now,
> it's past midnight ;-)
So I have been playing about with this a bit and it keeps falling short
of 'nice' :/
What I ended up with is the below. The simple scoped_guard () extension
is useful, albeit slightly awkward (I'll reply with another patch making
use of it). But the basic problem is that it will have to have the form:
scoped_guard (mutex_intr, &task->signal->cred_guard_mutex) {
...
return 0;
}
return -EINTR;
That is; the guard body must terminate such that after the body is the
'fail' case. This is not always convenient.
Additionally, this did not help with my case where I need to hold the
lock conditionally (when I have a task) but need to execute the body
unconditionally. Then the above form just doesn't work.
For that, I ended up with:
cond_guard(name, stmt, args...)
Which can be used like:
do {
cond_guard(rwsem_down_intr, if (task) return -EINTR,
task ? task->signal->exec_update_lock : NULL);
... do stuff that is conditionally guarded by @exec_update_lock ...
} while (0);
I'll continue poking for a bit,.. see if there's something better.
---
Subject: cleanup: Add conditional guard support
From: Peter Zijlstra <peterz@...radead.org>
Date: Sun Sep 17 13:22:17 CEST 2023
Adds:
- DEFINE_GUARD_COND() / DEFINE_LOCK_GUARD_1_COND() to extend existing
guards with conditional lock primitives, eg. mutex_trylock(),
mutex_lock_interruptible().
nb. both primitives allow NULL 'locks', which cause the lock to
fail (obviously).
- extends scoped_guard() to not take the body when the the
conditional guard 'fails'. eg.
scoped_guard (mutex_intr, &task->signal_cred_guard_mutex) {
...
}
will only execute the body when the mutex is held.
- provides cond_guard(name, stmt, args...); which extends guard()
to execute @stmt when the lock fails.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
Index: linux-2.6/include/linux/cleanup.h
===================================================================
--- linux-2.6.orig/include/linux/cleanup.h
+++ linux-2.6/include/linux/cleanup.h
@@ -136,14 +136,36 @@ static inline class_##_name##_t class_##
*/
#define DEFINE_GUARD(_name, _type, _lock, _unlock) \
- DEFINE_CLASS(_name, _type, _unlock, ({ _lock; _T; }), _type _T)
+ DEFINE_CLASS(_name, _type, if (_T) { _unlock; }, ({ _lock; _T; }), _type _T); \
+ static inline void * class_##_name##_lock_ptr(class_##_name##_t *_T) \
+ { return *_T; }
+
+#define DEFINE_GUARD_COND(_name, _ext, _condlock) \
+ EXTEND_CLASS(_name, _ext, \
+ ({ void *_t = _T; if (_T && !(_condlock)) _t = NULL; _t; }), \
+ class_##_name##_t _T) \
+ static inline void * class_##_name##_ext##_lock_ptr(class_##_name##_t *_T) \
+ { return class_##_name##_lock_ptr(_T); }
+
+#define _guard(_name, var) \
+ class_##_name##_t var __cleanup(class_##_name##_destructor) = \
+ class_##_name##_constructor
#define guard(_name) \
- CLASS(_name, __UNIQUE_ID(guard))
+ _guard(_name, __UNIQUE_ID(guard))
+
+#define __guard_ptr(_name) class_##_name##_lock_ptr
#define scoped_guard(_name, args...) \
for (CLASS(_name, scope)(args), \
- *done = NULL; !done; done = (void *)1)
+ *done = NULL; __guard_ptr(_name)(&scope) && !done; done = (void *)1)
+
+#define _cond_guard(_name, _var, _stmt, args...) \
+ _guard(_name, _var)(args); \
+ if (!__guard_ptr(_name)(&_var)) _stmt
+
+#define cond_guard(_name, _stmt, args...) \
+ _cond_guard(_name, __UNIQUE_ID(guard), _stmt, args)
/*
* Additional helper macros for generating lock guards with types, either for
@@ -173,6 +195,11 @@ typedef struct { \
static inline void class_##_name##_destructor(class_##_name##_t *_T) \
{ \
if (_T->lock) { _unlock; } \
+} \
+ \
+static inline void *class_##_name##_lock_ptr(class_##_name##_t *_T) \
+{ \
+ return _T->lock; \
}
@@ -201,4 +228,14 @@ __DEFINE_LOCK_GUARD_1(_name, _type, _loc
__DEFINE_UNLOCK_GUARD(_name, void, _unlock, __VA_ARGS__) \
__DEFINE_LOCK_GUARD_0(_name, _lock)
+#define DEFINE_LOCK_GUARD_1_COND(_name, _ext, _condlock) \
+ EXTEND_CLASS(_name, _ext, \
+ ({ class_##_name##_t _t = { .lock = l }, *_T = &_t;\
+ if (_T->lock && !(_condlock)) _T->lock = NULL; \
+ _t; }), \
+ typeof_member(class_##_name##_t, lock) l) \
+ static inline void * class_##_name##_ext##_lock_ptr(class_##_name##_t *_T) \
+ { return class_##_name##_lock_ptr(_T); }
+
+
#endif /* __LINUX_GUARDS_H */
Index: linux-2.6/include/linux/mutex.h
===================================================================
--- linux-2.6.orig/include/linux/mutex.h
+++ linux-2.6/include/linux/mutex.h
@@ -221,6 +221,7 @@ extern void mutex_unlock(struct mutex *l
extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
DEFINE_GUARD(mutex, struct mutex *, mutex_lock(_T), mutex_unlock(_T))
-DEFINE_FREE(mutex, struct mutex *, if (_T) mutex_unlock(_T))
+DEFINE_GUARD_COND(mutex, _try, mutex_trylock(_T))
+DEFINE_GUARD_COND(mutex, _intr, mutex_lock_interruptible(_T) == 0)
#endif /* __LINUX_MUTEX_H */
Index: linux-2.6/include/linux/spinlock.h
===================================================================
--- linux-2.6.orig/include/linux/spinlock.h
+++ linux-2.6/include/linux/spinlock.h
@@ -507,6 +507,8 @@ DEFINE_LOCK_GUARD_1(raw_spinlock, raw_sp
raw_spin_lock(_T->lock),
raw_spin_unlock(_T->lock))
+DEFINE_LOCK_GUARD_1_COND(raw_spinlock, _try, raw_spin_trylock(_T->lock))
+
DEFINE_LOCK_GUARD_1(raw_spinlock_nested, raw_spinlock_t,
raw_spin_lock_nested(_T->lock, SINGLE_DEPTH_NESTING),
raw_spin_unlock(_T->lock))
@@ -515,23 +517,36 @@ DEFINE_LOCK_GUARD_1(raw_spinlock_irq, ra
raw_spin_lock_irq(_T->lock),
raw_spin_unlock_irq(_T->lock))
+DEFINE_LOCK_GUARD_1_COND(raw_spinlock_irq, _try, raw_spin_trylock_irq(_T->lock))
+
DEFINE_LOCK_GUARD_1(raw_spinlock_irqsave, raw_spinlock_t,
raw_spin_lock_irqsave(_T->lock, _T->flags),
raw_spin_unlock_irqrestore(_T->lock, _T->flags),
unsigned long flags)
+DEFINE_LOCK_GUARD_1_COND(raw_spinlock_irqsave, _try,
+ raw_spin_trylock_irqsave(_T->lock, _T->flags))
+
DEFINE_LOCK_GUARD_1(spinlock, spinlock_t,
spin_lock(_T->lock),
spin_unlock(_T->lock))
+DEFINE_LOCK_GUARD_1_COND(spinlock, _try, spin_trylock(_T->lock))
+
DEFINE_LOCK_GUARD_1(spinlock_irq, spinlock_t,
spin_lock_irq(_T->lock),
spin_unlock_irq(_T->lock))
+DEFINE_LOCK_GUARD_1_COND(spinlock_irq, _try,
+ spin_trylock_irq(_T->lock))
+
DEFINE_LOCK_GUARD_1(spinlock_irqsave, spinlock_t,
spin_lock_irqsave(_T->lock, _T->flags),
spin_unlock_irqrestore(_T->lock, _T->flags),
unsigned long flags)
+DEFINE_LOCK_GUARD_1_COND(spinlock_irqsave, _try,
+ spin_trylock_irqsave(_T->lock, _T->flags))
+
#undef __LINUX_INSIDE_SPINLOCK_H
#endif /* __LINUX_SPINLOCK_H */
Index: linux-2.6/include/linux/rwsem.h
===================================================================
--- linux-2.6.orig/include/linux/rwsem.h
+++ linux-2.6/include/linux/rwsem.h
@@ -203,11 +203,11 @@ extern void up_read(struct rw_semaphore
extern void up_write(struct rw_semaphore *sem);
DEFINE_GUARD(rwsem_read, struct rw_semaphore *, down_read(_T), up_read(_T))
-DEFINE_GUARD(rwsem_write, struct rw_semaphore *, down_write(_T), up_write(_T))
-
-DEFINE_FREE(up_read, struct rw_semaphore *, if (_T) up_read(_T))
-DEFINE_FREE(up_write, struct rw_semaphore *, if (_T) up_write(_T))
+DEFINE_GUARD_COND(rwsem_read, _try, down_read_trylock(_T))
+DEFINE_GUARD_COND(rwsem_read, _intr, down_read_interruptible(_T) == 0)
+DEFINE_GUARD(rwsem_write, struct rw_semaphore *, down_write(_T), up_write(_T))
+DEFINE_GUARD_COND(rwsem_write, _try, down_write_trylock(_T))
/*
* downgrade write lock to read lock
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