futex: Replace PF_EXITPIDONE with a state (3d4775df) · Commits · 戴 / test

include/linux/futex.h

+33 −0

Original line number	Diff line number	Diff line
		@@ -50,6 +50,10 @@ union futex_key {
		#define FUTEX_KEY_INIT (union futex_key) { .both = { .ptr = NULL } }

		#ifdef CONFIG_FUTEX
		enum {
		FUTEX_STATE_OK,
		FUTEX_STATE_DEAD,
		};

		static inline void futex_init_task(struct task_struct *tsk)
		{
		@@ -59,6 +63,34 @@ static inline void futex_init_task(struct task_struct *tsk)
		#endif
		INIT_LIST_HEAD(&tsk->pi_state_list);
		tsk->pi_state_cache = NULL;
		tsk->futex_state = FUTEX_STATE_OK;
		}

		/**
		* futex_exit_done - Sets the tasks futex state to FUTEX_STATE_DEAD
		* @tsk: task to set the state on
		*
		* Set the futex exit state of the task lockless. The futex waiter code
		* observes that state when a task is exiting and loops until the task has
		* actually finished the futex cleanup. The worst case for this is that the
		* waiter runs through the wait loop until the state becomes visible.
		*
		* This has two callers:
		*
		* - futex_mm_release() after the futex exit cleanup has been done
		*
		* - do_exit() from the recursive fault handling path.
		*
		* In case of a recursive fault this is best effort. Either the futex exit
		* code has run already or not. If the OWNER_DIED bit has been set on the
		* futex then the waiter can take it over. If not, the problem is pushed
		* back to user space. If the futex exit code did not run yet, then an
		* already queued waiter might block forever, but there is nothing which
		* can be done about that.
		*/
		static inline void futex_exit_done(struct task_struct *tsk)
		{
		tsk->futex_state = FUTEX_STATE_DEAD;
		}

		void futex_mm_release(struct task_struct *tsk);
		@@ -68,6 +100,7 @@ long do_futex(u32 __user uaddr, int op, u32 val, ktime_t timeout,
		#else
		static inline void futex_init_task(struct task_struct *tsk) { }
		static inline void futex_mm_release(struct task_struct *tsk) { }
		static inline void futex_exit_done(struct task_struct *tsk) { }
		static inline long do_futex(u32 __user *uaddr, int op, u32 val,
		ktime_t timeout, u32 __user uaddr2,
		u32 val2, u32 val3)

include/linux/sched.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -1053,6 +1053,7 @@ struct task_struct {
		#endif
		struct list_head pi_state_list;
		struct futex_pi_state *pi_state_cache;
		unsigned int futex_state;
		#endif
		#ifdef CONFIG_PERF_EVENTS
		struct perf_event_context *perf_event_ctxp[perf_nr_task_contexts];
		@@ -1441,7 +1442,6 @@ extern struct pid *cad_pid;
		*/
		#define PF_IDLE 0x00000002 /* I am an IDLE thread */
		#define PF_EXITING 0x00000004 /* Getting shut down */
		#define PF_EXITPIDONE 0x00000008 /* PI exit done on shut down */
		#define PF_VCPU 0x00000010 /* I'm a virtual CPU */
		#define PF_WQ_WORKER 0x00000020 /* I'm a workqueue worker */
		#define PF_FORKNOEXEC 0x00000040 /* Forked but didn't exec */

kernel/exit.c

+2 −16

Original line number	Diff line number	Diff line
		@@ -746,16 +746,7 @@ void __noreturn do_exit(long code)
		*/
		if (unlikely(tsk->flags & PF_EXITING)) {
		pr_alert("Fixing recursive fault but reboot is needed!\n");
		/*
		* We can do this unlocked here. The futex code uses
		* this flag just to verify whether the pi state
		* cleanup has been done or not. In the worst case it
		* loops once more. We pretend that the cleanup was
		* done as there is no way to return. Either the
		* OWNER_DIED bit is set by now or we push the blocked
		* task into the wait for ever nirwana as well.
		*/
		tsk->flags \|= PF_EXITPIDONE;
		futex_exit_done(tsk);
		set_current_state(TASK_UNINTERRUPTIBLE);
		schedule();
		}
		@@ -846,12 +837,7 @@ void __noreturn do_exit(long code)
		* Make sure we are holding no locks:
		*/
		debug_check_no_locks_held();
		/*
		* We can do this unlocked here. The futex code uses this flag
		* just to verify whether the pi state cleanup has been done
		* or not. In the worst case it loops once more.
		*/
		tsk->flags \|= PF_EXITPIDONE;
		futex_exit_done(tsk);

		if (tsk->io_context)
		exit_io_context(tsk);

kernel/futex.c

+13 −12

Original line number	Diff line number	Diff line
		@@ -1182,9 +1182,10 @@ static int handle_exit_race(u32 __user *uaddr, u32 uval,
		u32 uval2;

		/*
		* If PF_EXITPIDONE is not yet set, then try again.
		* If the futex exit state is not yet FUTEX_STATE_DEAD, wait
		* for it to finish.
		*/
		if (tsk && !(tsk->flags & PF_EXITPIDONE))
		if (tsk && tsk->futex_state != FUTEX_STATE_DEAD)
		return -EAGAIN;

		/*
		@@ -1203,8 +1204,9 @@ static int handle_exit_race(u32 __user *uaddr, u32 uval,
		* *uaddr = 0xC0000000; tsk = get_task(PID);
		* } if (!tsk->flags & PF_EXITING) {
		* ... attach();
		* tsk->flags \|= PF_EXITPIDONE; } else {
		* if (!(tsk->flags & PF_EXITPIDONE))
		* tsk->futex_state = } else {
		* FUTEX_STATE_DEAD; if (tsk->futex_state !=
		* FUTEX_STATE_DEAD)
		* return -EAGAIN;
		* return -ESRCH; <--- FAIL
		* }
		@@ -1260,17 +1262,16 @@ static int attach_to_pi_owner(u32 __user uaddr, u32 uval, union futex_key key,
		}

		/*
		* We need to look at the task state flags to figure out,
		* whether the task is exiting. To protect against the do_exit
		* change of the task flags, we do this protected by
		* p->pi_lock:
		* We need to look at the task state to figure out, whether the
		* task is exiting. To protect against the change of the task state
		* in futex_exit_release(), we do this protected by p->pi_lock:
		*/
		raw_spin_lock_irq(&p->pi_lock);
		if (unlikely(p->flags & PF_EXITING)) {
		if (unlikely(p->futex_state != FUTEX_STATE_OK)) {
		/*
		* The task is on the way out. When PF_EXITPIDONE is
		* set, we know that the task has finished the
		* cleanup:
		* The task is on the way out. When the futex state is
		* FUTEX_STATE_DEAD, we know that the task has finished
		* the cleanup:
		*/
		int ret = handle_exit_race(uaddr, uval, p);

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