Re: [linux-pm] [RFC][PATCH -mm 1/5] PM: Make freeze_processes SMP-safe

Pavel Machek
2006-11-26T19:45:39Z

Hi!

> > Okay, I'll use atomic_t.
>
> Patch with atomic_t follows.
>
> The atomic_set(..., 0) are used to avoid the (theoretical) situation in which
> freezing might be decreased twice in a row and I've decided to explicitly
> initialize freezing in fork.c for clarity.

Looks okay to me, but I'm not sure if Andrew/someone will not have a
problem with task_struct getting bigger. Can you push this one early
and separately?

Pavel

> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
> ---
> include/linux/freezer.h | 10 +++++-----
> include/linux/sched.h | 4 +++-
> kernel/fork.c | 4 ++++
> 3 files changed, 12 insertions(+), 6 deletions(-)
>
> Index: linux-2.6.19-rc6-mm1/include/linux/freezer.h
> ===================================================================
> --- linux-2.6.19-rc6-mm1.orig/include/linux/freezer.h 2006-11-26 11:31:39.000000000 +0100
> +++ linux-2.6.19-rc6-mm1/include/linux/freezer.h 2006-11-26 11:52:29.000000000 +0100
> @@ -14,16 +14,15 @@ static inline int frozen(struct task_str
> */
> static inline int freezing(struct task_struct *p)
> {
> - return p->flags & PF_FREEZE;
> + return !!atomic_read(&p->freezing);
> }
>
> /*
> * 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;
> + atomic_inc(&p->freezing);
> }
>
> /*
> @@ -31,7 +30,7 @@ static inline void freeze(struct task_st
> */
> static inline void do_not_freeze(struct task_struct *p)
> {
> - p->flags &= ~PF_FREEZE;
> + atomic_set(&p->freezing, 0);
> }
>
> /*
> @@ -52,7 +51,8 @@ static inline int thaw_process(struct ta
> */
> static inline void frozen_process(struct task_struct *p)
> {
> - p->flags = (p->flags & ~PF_FREEZE) | PF_FROZEN;
> + p->flags |= PF_FROZEN;
> + atomic_set(&p->freezing, 0);
> }
>
> extern void refrigerator(void);
> Index: linux-2.6.19-rc6-mm1/include/linux/sched.h
> ===================================================================
> --- linux-2.6.19-rc6-mm1.orig/include/linux/sched.h 2006-11-26 11:31:39.000000000 +0100
> +++ linux-2.6.19-rc6-mm1/include/linux/sched.h 2006-11-26 11:33:29.000000000 +0100
> @@ -1065,6 +1065,9 @@ struct task_struct {
> #ifdef CONFIG_TASK_DELAY_ACCT
> struct task_delay_info *delays;
> #endif
> +#ifdef CONFIG_PM
> + atomic_t freezing; /* if set, we should be freezing for suspend */
> +#endif
> #ifdef CONFIG_FAULT_INJECTION
> int make_it_fail;
> #endif
> @@ -1161,7 +1164,6 @@ static inline void put_task_struct(struc
> #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 */
> Index: linux-2.6.19-rc6-mm1/kernel/fork.c
> ===================================================================
> --- linux-2.6.19-rc6-mm1.orig/kernel/fork.c 2006-11-25 21:26:52.000000000 +0100
> +++ linux-2.6.19-rc6-mm1/kernel/fork.c 2006-11-26 11:45:00.000000000 +0100
> @@ -1097,6 +1097,10 @@ static struct task_struct *copy_process(
> p->blocked_on = NULL; /* not blocked yet */
> #endif
>
> +#ifdef CONFIG_PM
> + atomic_set(&p->freezing, 0);
> +#endif
> +
> p->tgid = p->pid;
> if (clone_flags & CLONE_THREAD)
> p->tgid = current->tgid;
> _______________________________________________
> linux-pm mailing list
> linux-pm@lists.osdl.org
> https://lists.osdl.org/mailman/listinfo/linux-pm

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