From 42aaa0cc9e4142f108001da3bb8cad701f533423 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Thu, 22 Oct 2015 09:03:58 +1100 Subject: [PATCH] signals: kill block_all_signals() and unblock_all_signals() It is hardly possible to enumerate all problems with block_all_signals() and unblock_all_signals(). Just for example, 1. block_all_signals(SIGSTOP/etc) simply can't help if the caller is multithreaded. Another thread can dequeue the signal and force the group stop. 2. Even is the caller is single-threaded, it will "stop" anyway. It will not sleep, but it will spin in kernel space until SIGCONT or SIGKILL. And a lot more. In short, this interface doesn't work at all, at least the last 10+ years. Daniel said: Yeah the only times I played around with the DRM_LOCK stuff was when old drivers accidentally deadlocked - my impression is that the entire DRM_LOCK thing was never really tested properly ;-) Hence I'm all for purging where this leaks out of the drm subsystem. Signed-off-by: Oleg Nesterov Acked-by: Daniel Vetter Acked-by: Dave Airlie Cc: Richard Weinberger Signed-off-by: Andrew Morton --- drivers/gpu/drm/drm_lock.c | 41 ------------------------------ include/drm/drmP.h | 1 - include/linux/sched.h | 7 +----- kernel/signal.c | 51 +------------------------------------- 4 files changed, 2 insertions(+), 98 deletions(-) diff --git a/drivers/gpu/drm/drm_lock.c b/drivers/gpu/drm/drm_lock.c index 4924d381b664..daa2ff12101b 100644 --- a/drivers/gpu/drm/drm_lock.c +++ b/drivers/gpu/drm/drm_lock.c @@ -38,8 +38,6 @@ #include "drm_legacy.h" #include "drm_internal.h" -static int drm_notifier(void *priv); - static int drm_lock_take(struct drm_lock_data *lock_data, unsigned int context); /** @@ -118,14 +116,8 @@ int drm_legacy_lock(struct drm_device *dev, void *data, * really probably not the correct answer but lets us debug xkb * xserver for now */ if (!file_priv->is_master) { - sigemptyset(&dev->sigmask); - sigaddset(&dev->sigmask, SIGSTOP); - sigaddset(&dev->sigmask, SIGTSTP); - sigaddset(&dev->sigmask, SIGTTIN); - sigaddset(&dev->sigmask, SIGTTOU); dev->sigdata.context = lock->context; dev->sigdata.lock = master->lock.hw_lock; - block_all_signals(drm_notifier, dev, &dev->sigmask); } if (dev->driver->dma_quiescent && (lock->flags & _DRM_LOCK_QUIESCENT)) @@ -169,7 +161,6 @@ int drm_legacy_unlock(struct drm_device *dev, void *data, struct drm_file *file_ /* FIXME: Should really bail out here. */ } - unblock_all_signals(); return 0; } @@ -287,38 +278,6 @@ int drm_legacy_lock_free(struct drm_lock_data *lock_data, unsigned int context) return 0; } -/** - * If we get here, it means that the process has called DRM_IOCTL_LOCK - * without calling DRM_IOCTL_UNLOCK. - * - * If the lock is not held, then let the signal proceed as usual. If the lock - * is held, then set the contended flag and keep the signal blocked. - * - * \param priv pointer to a drm_device structure. - * \return one if the signal should be delivered normally, or zero if the - * signal should be blocked. - */ -static int drm_notifier(void *priv) -{ - struct drm_device *dev = priv; - struct drm_hw_lock *lock = dev->sigdata.lock; - unsigned int old, new, prev; - - /* Allow signal delivery if lock isn't held */ - if (!lock || !_DRM_LOCK_IS_HELD(lock->lock) - || _DRM_LOCKING_CONTEXT(lock->lock) != dev->sigdata.context) - return 1; - - /* Otherwise, set flag to force call to - drmUnlock */ - do { - old = lock->lock; - new = old | _DRM_LOCK_CONT; - prev = cmpxchg(&lock->lock, old, new); - } while (prev != old); - return 0; -} - /** * This function returns immediately and takes the hw lock * with the kernel context if it is free, otherwise it gets the highest priority when and if diff --git a/include/drm/drmP.h b/include/drm/drmP.h index 8b5ce7c5d9bb..f56cdcecc1c9 100644 --- a/include/drm/drmP.h +++ b/include/drm/drmP.h @@ -822,7 +822,6 @@ struct drm_device { struct drm_sg_mem *sg; /**< Scatter gather memory */ unsigned int num_crtcs; /**< Number of CRTCs on this device */ - sigset_t sigmask; struct { int context; diff --git a/include/linux/sched.h b/include/linux/sched.h index 8a6829af53a2..a21197572391 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1573,9 +1573,7 @@ struct task_struct { unsigned long sas_ss_sp; size_t sas_ss_size; - int (*notifier)(void *priv); - void *notifier_data; - sigset_t *notifier_mask; + struct callback_head *task_works; struct audit_context *audit_context; @@ -2479,9 +2477,6 @@ static inline int dequeue_signal_lock(struct task_struct *tsk, sigset_t *mask, s return ret; } -extern void block_all_signals(int (*notifier)(void *priv), void *priv, - sigset_t *mask); -extern void unblock_all_signals(void); extern void release_task(struct task_struct * p); extern int send_sig_info(int, struct siginfo *, struct task_struct *); extern int force_sigsegv(int, struct task_struct *); diff --git a/kernel/signal.c b/kernel/signal.c index 0f6bbbe77b46..f2cbd4ed5cd4 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -503,41 +503,6 @@ int unhandled_signal(struct task_struct *tsk, int sig) return !tsk->ptrace; } -/* - * Notify the system that a driver wants to block all signals for this - * process, and wants to be notified if any signals at all were to be - * sent/acted upon. If the notifier routine returns non-zero, then the - * signal will be acted upon after all. If the notifier routine returns 0, - * then then signal will be blocked. Only one block per process is - * allowed. priv is a pointer to private data that the notifier routine - * can use to determine if the signal should be blocked or not. - */ -void -block_all_signals(int (*notifier)(void *priv), void *priv, sigset_t *mask) -{ - unsigned long flags; - - spin_lock_irqsave(¤t->sighand->siglock, flags); - current->notifier_mask = mask; - current->notifier_data = priv; - current->notifier = notifier; - spin_unlock_irqrestore(¤t->sighand->siglock, flags); -} - -/* Notify the system that blocking has ended. */ - -void -unblock_all_signals(void) -{ - unsigned long flags; - - spin_lock_irqsave(¤t->sighand->siglock, flags); - current->notifier = NULL; - current->notifier_data = NULL; - recalc_sigpending(); - spin_unlock_irqrestore(¤t->sighand->siglock, flags); -} - static void collect_signal(int sig, struct sigpending *list, siginfo_t *info) { struct sigqueue *q, *first = NULL; @@ -580,19 +545,8 @@ static int __dequeue_signal(struct sigpending *pending, sigset_t *mask, { int sig = next_signal(pending, mask); - if (sig) { - if (current->notifier) { - if (sigismember(current->notifier_mask, sig)) { - if (!(current->notifier)(current->notifier_data)) { - clear_thread_flag(TIF_SIGPENDING); - return 0; - } - } - } - + if (sig) collect_signal(sig, pending, info); - } - return sig; } @@ -2483,9 +2437,6 @@ EXPORT_SYMBOL(force_sig); EXPORT_SYMBOL(send_sig); EXPORT_SYMBOL(send_sig_info); EXPORT_SYMBOL(sigprocmask); -EXPORT_SYMBOL(block_all_signals); -EXPORT_SYMBOL(unblock_all_signals); - /* * System call entry points. -- 2.39.5