From: Rafael J. Wysocki Date: Wed, 13 Dec 2006 08:34:30 +0000 (-0800) Subject: [PATCH] PM: Fix SMP races in the freezer X-Git-Tag: v2.6.20-rc1~98 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8a102eed9c4e1d21bad07a8fd97bd4fbf125d966;p=linux-2.6 [PATCH] PM: Fix SMP races in the freezer Currently, to tell a task that it should go to the refrigerator, we set the PF_FREEZE flag for it and send a fake signal to it. Unfortunately there are two SMP-related problems with this approach. First, a task running on another CPU may be updating its flags while the freezer attempts to set PF_FREEZE for it and this may leave the task's flags in an inconsistent state. Second, there is a potential race between freeze_process() and refrigerator() in which freeze_process() running on one CPU is reading a task's PF_FREEZE flag while refrigerator() running on another CPU has just set PF_FROZEN for the same task and attempts to reset PF_FREEZE for it. If the refrigerator wins the race, freeze_process() will state that PF_FREEZE hasn't been set for the task and will set it unnecessarily, so the task will go to the refrigerator once again after it's been thawed. To solve first of these problems we need to stop using PF_FREEZE to tell tasks that they should go to the refrigerator. Instead, we can introduce a special TIF_*** flag and use it for this purpose, since it is allowed to change the other tasks' TIF_*** flags and there are special calls for it. To avoid the freeze_process()-refrigerator() race we can make freeze_process() to always check the task's PF_FROZEN flag after it's read its "freeze" flag. We should also make sure that refrigerator() will always reset the task's "freeze" flag after it's set PF_FROZEN for it. Signed-off-by: Rafael J. Wysocki Acked-by: Pavel Machek Cc: Russell King Cc: David Howells Cc: Andi Kleen Cc: "Luck, Tony" Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: Paul Mundt Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/include/asm-arm/thread_info.h b/include/asm-arm/thread_info.h index d9b8bddc87..5014794f9e 100644 --- a/include/asm-arm/thread_info.h +++ b/include/asm-arm/thread_info.h @@ -147,6 +147,7 @@ extern void iwmmxt_task_switch(struct thread_info *); #define TIF_POLLING_NRFLAG 16 #define TIF_USING_IWMMXT 17 #define TIF_MEMDIE 18 +#define TIF_FREEZE 19 #define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME) #define _TIF_SIGPENDING (1 << TIF_SIGPENDING) @@ -154,6 +155,7 @@ extern void iwmmxt_task_switch(struct thread_info *); #define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE) #define _TIF_POLLING_NRFLAG (1 << TIF_POLLING_NRFLAG) #define _TIF_USING_IWMMXT (1 << TIF_USING_IWMMXT) +#define _TIF_FREEZE (1 << TIF_FREEZE) /* * Change these and you break ASM code in entry-common.S diff --git a/include/asm-frv/thread_info.h b/include/asm-frv/thread_info.h index d66c48e6ef..d881f518e6 100644 --- a/include/asm-frv/thread_info.h +++ b/include/asm-frv/thread_info.h @@ -116,6 +116,7 @@ register struct thread_info *__current_thread_info asm("gr15"); #define TIF_RESTORE_SIGMASK 6 /* restore signal mask in do_signal() */ #define TIF_POLLING_NRFLAG 16 /* true if poll_idle() is polling TIF_NEED_RESCHED */ #define TIF_MEMDIE 17 /* OOM killer killed process */ +#define TIF_FREEZE 18 /* freezing for suspend */ #define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE) #define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME) @@ -125,6 +126,7 @@ register struct thread_info *__current_thread_info asm("gr15"); #define _TIF_IRET (1 << TIF_IRET) #define _TIF_RESTORE_SIGMASK (1 << TIF_RESTORE_SIGMASK) #define _TIF_POLLING_NRFLAG (1 << TIF_POLLING_NRFLAG) +#define _TIF_FREEZE (1 << TIF_FREEZE) #define _TIF_WORK_MASK 0x0000FFFE /* work to do on interrupt/exception return */ #define _TIF_ALLWORK_MASK 0x0000FFFF /* work to do on any return to u-space */ diff --git a/include/asm-i386/thread_info.h b/include/asm-i386/thread_info.h index 46d32ad920..4b187bb377 100644 --- a/include/asm-i386/thread_info.h +++ b/include/asm-i386/thread_info.h @@ -134,6 +134,7 @@ static inline struct thread_info *current_thread_info(void) #define TIF_MEMDIE 16 #define TIF_DEBUG 17 /* uses debug registers */ #define TIF_IO_BITMAP 18 /* uses I/O bitmap */ +#define TIF_FREEZE 19 /* is freezing for suspend */ #define _TIF_SYSCALL_TRACE (1<flags & PF_FREEZE; + return test_tsk_thread_flag(p, TIF_FREEZE); } /* * Request that a process be frozen - * FIXME: SMP problem. We may not modify other process' flags! */ static inline void freeze(struct task_struct *p) { - p->flags |= PF_FREEZE; + set_tsk_thread_flag(p, TIF_FREEZE); } /* @@ -33,7 +32,7 @@ static inline void freeze(struct task_struct *p) */ static inline void do_not_freeze(struct task_struct *p) { - p->flags &= ~PF_FREEZE; + clear_tsk_thread_flag(p, TIF_FREEZE); } /* @@ -54,7 +53,9 @@ static inline int thaw_process(struct task_struct *p) */ static inline void frozen_process(struct task_struct *p) { - p->flags = (p->flags & ~PF_FREEZE) | PF_FROZEN; + p->flags |= PF_FROZEN; + wmb(); + clear_tsk_thread_flag(p, TIF_FREEZE); } extern void refrigerator(void); diff --git a/include/linux/sched.h b/include/linux/sched.h index ea92e5c890..4463735351 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1144,7 +1144,6 @@ static inline void put_task_struct(struct task_struct *t) #define PF_MEMALLOC 0x00000800 /* Allocating memory */ #define PF_FLUSHER 0x00001000 /* responsible for disk writeback */ #define PF_USED_MATH 0x00002000 /* if unset the fpu must be initialized before use */ -#define PF_FREEZE 0x00004000 /* this task is being frozen for suspend now */ #define PF_NOFREEZE 0x00008000 /* this thread should not be frozen */ #define PF_FROZEN 0x00010000 /* frozen for system suspend */ #define PF_FSTRANS 0x00020000 /* inside a filesystem transaction */ diff --git a/kernel/power/process.c b/kernel/power/process.c index b9a32860be..6d566bf708 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -60,13 +60,16 @@ static inline void freeze_process(struct task_struct *p) unsigned long flags; if (!freezing(p)) { - if (p->state == TASK_STOPPED) - force_sig_specific(SIGSTOP, p); - - freeze(p); - spin_lock_irqsave(&p->sighand->siglock, flags); - signal_wake_up(p, p->state == TASK_STOPPED); - spin_unlock_irqrestore(&p->sighand->siglock, flags); + rmb(); + if (!frozen(p)) { + if (p->state == TASK_STOPPED) + force_sig_specific(SIGSTOP, p); + + freeze(p); + spin_lock_irqsave(&p->sighand->siglock, flags); + signal_wake_up(p, p->state == TASK_STOPPED); + spin_unlock_irqrestore(&p->sighand->siglock, flags); + } } }