diff options
author | Thomas Gleixner <tglx@linutronix.de> | 2019-11-06 22:55:37 +0100 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-01-30 13:32:11 +0100 |
commit | 095444fad7e35dcd63d0c6b86461d024314e2051 (patch) | |
tree | e9e82c222301b47d928f19775a32e23cbb9fc90b /include | |
parent | 3fe0ed7bd7329e28aca7cdaf7353c6d4778b3d41 (diff) |
futex: Replace PF_EXITPIDONE with a state
commit 3d4775df0a89240f671861c6ab6e8d59af8e9e41 upstream
The futex exit handling relies on PF_ flags. That's suboptimal as it
requires a smp_mb() and an ugly lock/unlock of the exiting tasks pi_lock in
the middle of do_exit() to enforce the observability of PF_EXITING in the
futex code.
Add a futex_state member to task_struct and convert the PF_EXITPIDONE logic
over to the new state. The PF_EXITING dependency will be cleaned up in a
later step.
This prepares for handling various futex exit issues later.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20191106224556.149449274@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include')
-rw-r--r-- | include/linux/futex.h | 33 | ||||
-rw-r--r-- | include/linux/sched.h | 2 |
2 files changed, 34 insertions, 1 deletions
diff --git a/include/linux/futex.h b/include/linux/futex.h index 82b8a5cd4018..84e945116126 100644 --- a/include/linux/futex.h +++ b/include/linux/futex.h @@ -53,6 +53,10 @@ union futex_key { #define FUTEX_KEY_INIT (union futex_key) { .both = { .ptr = 0ULL } } #ifdef CONFIG_FUTEX +enum { + FUTEX_STATE_OK, + FUTEX_STATE_DEAD, +}; static inline void futex_init_task(struct task_struct *tsk) { @@ -62,6 +66,34 @@ 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); @@ -71,6 +103,7 @@ 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) diff --git a/include/linux/sched.h b/include/linux/sched.h index c69f308f3a53..f343a2bc913c 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -996,6 +996,7 @@ 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]; @@ -1377,7 +1378,6 @@ 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 */ |