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52400ba946
PI Futexes and their underlying rt_mutex cannot be left ownerless if there are pending waiters as this will break the PI boosting logic, so the standard requeue commands aren't sufficient. The new commands properly manage pi futex ownership by ensuring a futex with waiters has an owner at all times. This will allow glibc to properly handle pi mutexes with pthread_condvars. The approach taken here is to create two new futex op codes: FUTEX_WAIT_REQUEUE_PI: Tasks will use this op code to wait on a futex (such as a non-pi waitqueue) and wake after they have been requeued to a pi futex. Prior to returning to userspace, they will acquire this pi futex (and the underlying rt_mutex). futex_wait_requeue_pi() is the result of a high speed collision between futex_wait() and futex_lock_pi() (with the first part of futex_lock_pi() being done by futex_proxy_trylock_atomic() on behalf of the top_waiter). FUTEX_REQUEUE_PI (and FUTEX_CMP_REQUEUE_PI): This call must be used to wake tasks waiting with FUTEX_WAIT_REQUEUE_PI, regardless of how many tasks the caller intends to wake or requeue. pthread_cond_broadcast() should call this with nr_wake=1 and nr_requeue=INT_MAX. pthread_cond_signal() should call this with nr_wake=1 and nr_requeue=0. The reason being we need both callers to get the benefit of the futex_proxy_trylock_atomic() routine. futex_requeue() also enqueues the top_waiter on the rt_mutex via rt_mutex_start_proxy_lock(). Signed-off-by: Darren Hart <dvhltc@us.ibm.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
132 lines
3.4 KiB
C
132 lines
3.4 KiB
C
/* thread_info.h: common low-level thread information accessors
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*
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* Copyright (C) 2002 David Howells (dhowells@redhat.com)
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* - Incorporating suggestions made by Linus Torvalds
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*/
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#ifndef _LINUX_THREAD_INFO_H
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#define _LINUX_THREAD_INFO_H
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#include <linux/types.h>
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struct timespec;
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struct compat_timespec;
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/*
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* System call restart block.
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*/
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struct restart_block {
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long (*fn)(struct restart_block *);
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union {
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struct {
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unsigned long arg0, arg1, arg2, arg3;
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};
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/* For futex_wait and futex_wait_requeue_pi */
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struct {
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u32 *uaddr;
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u32 val;
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u32 flags;
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u32 bitset;
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u64 time;
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u32 *uaddr2;
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} futex;
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/* For nanosleep */
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struct {
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clockid_t index;
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struct timespec __user *rmtp;
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#ifdef CONFIG_COMPAT
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struct compat_timespec __user *compat_rmtp;
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#endif
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u64 expires;
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} nanosleep;
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/* For poll */
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struct {
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struct pollfd __user *ufds;
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int nfds;
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int has_timeout;
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unsigned long tv_sec;
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unsigned long tv_nsec;
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} poll;
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};
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};
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extern long do_no_restart_syscall(struct restart_block *parm);
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#include <linux/bitops.h>
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#include <asm/thread_info.h>
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#ifdef __KERNEL__
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/*
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* flag set/clear/test wrappers
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* - pass TIF_xxxx constants to these functions
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*/
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static inline void set_ti_thread_flag(struct thread_info *ti, int flag)
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{
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set_bit(flag, (unsigned long *)&ti->flags);
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}
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static inline void clear_ti_thread_flag(struct thread_info *ti, int flag)
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{
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clear_bit(flag, (unsigned long *)&ti->flags);
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}
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static inline int test_and_set_ti_thread_flag(struct thread_info *ti, int flag)
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{
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return test_and_set_bit(flag, (unsigned long *)&ti->flags);
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}
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static inline int test_and_clear_ti_thread_flag(struct thread_info *ti, int flag)
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{
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return test_and_clear_bit(flag, (unsigned long *)&ti->flags);
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}
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static inline int test_ti_thread_flag(struct thread_info *ti, int flag)
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{
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return test_bit(flag, (unsigned long *)&ti->flags);
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}
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#define set_thread_flag(flag) \
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set_ti_thread_flag(current_thread_info(), flag)
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#define clear_thread_flag(flag) \
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clear_ti_thread_flag(current_thread_info(), flag)
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#define test_and_set_thread_flag(flag) \
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test_and_set_ti_thread_flag(current_thread_info(), flag)
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#define test_and_clear_thread_flag(flag) \
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test_and_clear_ti_thread_flag(current_thread_info(), flag)
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#define test_thread_flag(flag) \
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test_ti_thread_flag(current_thread_info(), flag)
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#define set_need_resched() set_thread_flag(TIF_NEED_RESCHED)
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#define clear_need_resched() clear_thread_flag(TIF_NEED_RESCHED)
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#if defined TIF_RESTORE_SIGMASK && !defined HAVE_SET_RESTORE_SIGMASK
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/*
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* An arch can define its own version of set_restore_sigmask() to get the
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* job done however works, with or without TIF_RESTORE_SIGMASK.
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*/
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#define HAVE_SET_RESTORE_SIGMASK 1
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/**
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* set_restore_sigmask() - make sure saved_sigmask processing gets done
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*
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* This sets TIF_RESTORE_SIGMASK and ensures that the arch signal code
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* will run before returning to user mode, to process the flag. For
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* all callers, TIF_SIGPENDING is already set or it's no harm to set
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* it. TIF_RESTORE_SIGMASK need not be in the set of bits that the
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* arch code will notice on return to user mode, in case those bits
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* are scarce. We set TIF_SIGPENDING here to ensure that the arch
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* signal code always gets run when TIF_RESTORE_SIGMASK is set.
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*/
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static inline void set_restore_sigmask(void)
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{
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set_thread_flag(TIF_RESTORE_SIGMASK);
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set_thread_flag(TIF_SIGPENDING);
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}
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#endif /* TIF_RESTORE_SIGMASK && !HAVE_SET_RESTORE_SIGMASK */
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#endif /* __KERNEL__ */
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#endif /* _LINUX_THREAD_INFO_H */
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