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linux/include/asm-powerpc/thread_info.h
Rafael J. Wysocki 8a102eed9c [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 <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: David Howells <dhowells@redhat.com>
Cc: Andi Kleen <ak@muc.de>
Cc: "Luck, Tony" <tony.luck@intel.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-12-13 09:05:49 -08:00

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/* thread_info.h: PowerPC low-level thread information
* adapted from the i386 version by Paul Mackerras
*
* Copyright (C) 2002 David Howells (dhowells@redhat.com)
* - Incorporating suggestions made by Linus Torvalds and Dave Miller
*/
#ifndef _ASM_POWERPC_THREAD_INFO_H
#define _ASM_POWERPC_THREAD_INFO_H
#ifdef __KERNEL__
/* We have 8k stacks on ppc32 and 16k on ppc64 */
#ifdef CONFIG_PPC64
#define THREAD_SHIFT 14
#else
#define THREAD_SHIFT 13
#endif
#define THREAD_SIZE (1 << THREAD_SHIFT)
#ifndef __ASSEMBLY__
#include <linux/cache.h>
#include <asm/processor.h>
#include <asm/page.h>
#include <linux/stringify.h>
/*
* low level task data.
*/
struct thread_info {
struct task_struct *task; /* main task structure */
struct exec_domain *exec_domain; /* execution domain */
int cpu; /* cpu we're on */
int preempt_count; /* 0 => preemptable,
<0 => BUG */
struct restart_block restart_block;
unsigned long local_flags; /* private flags for thread */
/* low level flags - has atomic operations done on it */
unsigned long flags ____cacheline_aligned_in_smp;
};
/*
* macros/functions for gaining access to the thread information structure
*
* preempt_count needs to be 1 initially, until the scheduler is functional.
*/
#define INIT_THREAD_INFO(tsk) \
{ \
.task = &tsk, \
.exec_domain = &default_exec_domain, \
.cpu = 0, \
.preempt_count = 1, \
.restart_block = { \
.fn = do_no_restart_syscall, \
}, \
.flags = 0, \
}
#define init_thread_info (init_thread_union.thread_info)
#define init_stack (init_thread_union.stack)
/* thread information allocation */
#if THREAD_SHIFT >= PAGE_SHIFT
#define THREAD_ORDER (THREAD_SHIFT - PAGE_SHIFT)
#ifdef CONFIG_DEBUG_STACK_USAGE
#define alloc_thread_info(tsk) \
((struct thread_info *)__get_free_pages(GFP_KERNEL | \
__GFP_ZERO, THREAD_ORDER))
#else
#define alloc_thread_info(tsk) \
((struct thread_info *)__get_free_pages(GFP_KERNEL, THREAD_ORDER))
#endif
#define free_thread_info(ti) free_pages((unsigned long)ti, THREAD_ORDER)
#else /* THREAD_SHIFT < PAGE_SHIFT */
#ifdef CONFIG_DEBUG_STACK_USAGE
#define alloc_thread_info(tsk) kzalloc(THREAD_SIZE, GFP_KERNEL)
#else
#define alloc_thread_info(tsk) kmalloc(THREAD_SIZE, GFP_KERNEL)
#endif
#define free_thread_info(ti) kfree(ti)
#endif /* THREAD_SHIFT < PAGE_SHIFT */
/* how to get the thread information struct from C */
static inline struct thread_info *current_thread_info(void)
{
register unsigned long sp asm("r1");
/* gcc4, at least, is smart enough to turn this into a single
* rlwinm for ppc32 and clrrdi for ppc64 */
return (struct thread_info *)(sp & ~(THREAD_SIZE-1));
}
#endif /* __ASSEMBLY__ */
#define PREEMPT_ACTIVE 0x10000000
/*
* thread information flag bit numbers
*/
#define TIF_SYSCALL_TRACE 0 /* syscall trace active */
#define TIF_NOTIFY_RESUME 1 /* resumption notification requested */
#define TIF_SIGPENDING 2 /* signal pending */
#define TIF_NEED_RESCHED 3 /* rescheduling necessary */
#define TIF_POLLING_NRFLAG 4 /* true if poll_idle() is polling
TIF_NEED_RESCHED */
#define TIF_32BIT 5 /* 32 bit binary */
#define TIF_RUNLATCH 6 /* Is the runlatch enabled? */
#define TIF_ABI_PENDING 7 /* 32/64 bit switch needed */
#define TIF_SYSCALL_AUDIT 8 /* syscall auditing active */
#define TIF_SINGLESTEP 9 /* singlestepping active */
#define TIF_MEMDIE 10
#define TIF_SECCOMP 11 /* secure computing */
#define TIF_RESTOREALL 12 /* Restore all regs (implies NOERROR) */
#define TIF_NOERROR 14 /* Force successful syscall return */
#define TIF_RESTORE_SIGMASK 15 /* Restore signal mask in do_signal */
#define TIF_FREEZE 16 /* Freezing for suspend */
/* as above, but as bit values */
#define _TIF_SYSCALL_TRACE (1<<TIF_SYSCALL_TRACE)
#define _TIF_NOTIFY_RESUME (1<<TIF_NOTIFY_RESUME)
#define _TIF_SIGPENDING (1<<TIF_SIGPENDING)
#define _TIF_NEED_RESCHED (1<<TIF_NEED_RESCHED)
#define _TIF_POLLING_NRFLAG (1<<TIF_POLLING_NRFLAG)
#define _TIF_32BIT (1<<TIF_32BIT)
#define _TIF_RUNLATCH (1<<TIF_RUNLATCH)
#define _TIF_ABI_PENDING (1<<TIF_ABI_PENDING)
#define _TIF_SYSCALL_AUDIT (1<<TIF_SYSCALL_AUDIT)
#define _TIF_SINGLESTEP (1<<TIF_SINGLESTEP)
#define _TIF_SECCOMP (1<<TIF_SECCOMP)
#define _TIF_RESTOREALL (1<<TIF_RESTOREALL)
#define _TIF_NOERROR (1<<TIF_NOERROR)
#define _TIF_RESTORE_SIGMASK (1<<TIF_RESTORE_SIGMASK)
#define _TIF_FREEZE (1<<TIF_FREEZE)
#define _TIF_SYSCALL_T_OR_A (_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SECCOMP)
#define _TIF_USER_WORK_MASK (_TIF_NOTIFY_RESUME | _TIF_SIGPENDING | \
_TIF_NEED_RESCHED | _TIF_RESTORE_SIGMASK)
#define _TIF_PERSYSCALL_MASK (_TIF_RESTOREALL|_TIF_NOERROR)
/* Bits in local_flags */
/* Don't move TLF_NAPPING without adjusting the code in entry_32.S */
#define TLF_NAPPING 0 /* idle thread enabled NAP mode */
#define _TLF_NAPPING (1 << TLF_NAPPING)
#endif /* __KERNEL__ */
#endif /* _ASM_POWERPC_THREAD_INFO_H */
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