kernel/futex/pi.c

Source file repositories/reference/linux-study-clean/kernel/futex/pi.c

File Facts

System
Linux kernel
Corpus path
kernel/futex/pi.c
Extension
.c
Size
36005 bytes
Lines
1317
Domain
Core OS
Bucket
Scheduler, Processes, Timers, Sync, And Syscalls
Inferred role
Core OS: implementation source
Status
source implementation candidate

Why This File Exists

Core operating-system implementation surface: boot, tasks, memory, VFS, syscall-facing interfaces, synchronization, credentials, and isolation.

Dependency Surface

Detected Declarations

Annotated Snippet

if (!pi_state->owner) {
			/*
			 * No pi state owner, but the user space TID
			 * is not 0. Inconsistent state. [5]
			 */
			if (pid)
				goto out_einval;
			/*
			 * Take a ref on the state and return success. [4]
			 */
			goto out_attach;
		}

		/*
		 * If TID is 0, then either the dying owner has not
		 * yet executed exit_pi_state_list() or some waiter
		 * acquired the rtmutex in the pi state, but did not
		 * yet fixup the TID in user space.
		 *
		 * Take a ref on the state and return success. [6]
		 */
		if (!pid)
			goto out_attach;
	} else {
		/*
		 * If the owner died bit is not set, then the pi_state
		 * must have an owner. [7]
		 */
		if (!pi_state->owner)
			goto out_einval;
	}

	/*
	 * Bail out if user space manipulated the futex value. If pi
	 * state exists then the owner TID must be the same as the
	 * user space TID. [9/10]
	 */
	if (pid != task_pid_vnr(pi_state->owner))
		goto out_einval;

out_attach:
	get_pi_state(pi_state);
	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
	*ps = pi_state;
	return 0;

out_einval:
	ret = -EINVAL;
	goto out_error;

out_eagain:
	ret = -EAGAIN;
	goto out_error;

out_efault:
	ret = -EFAULT;
	goto out_error;

out_error:
	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
	return ret;
}

static int handle_exit_race(u32 __user *uaddr, u32 uval,
			    struct task_struct *tsk)
{
	u32 uval2;

	/*
	 * If the futex exit state is not yet FUTEX_STATE_DEAD, tell the
	 * caller that the alleged owner is busy.
	 */
	if (tsk && tsk->futex.state != FUTEX_STATE_DEAD)
		return -EBUSY;

	/*
	 * Reread the user space value to handle the following situation:
	 *
	 * CPU0				CPU1
	 *
	 * sys_exit()			sys_futex()
	 *  do_exit()			 futex_lock_pi()
	 *                                futex_lock_pi_atomic()
	 *   exit_signals(tsk)		    No waiters:
	 *    tsk->flags |= PF_EXITING;	    *uaddr == 0x00000PID
	 *  mm_release(tsk)		    Set waiter bit
	 *   exit_robust_list(tsk) {	    *uaddr = 0x80000PID;
	 *      Set owner died		    attach_to_pi_owner() {
	 *    *uaddr = 0xC0000000;	     tsk = get_task(PID);
	 *   }				     if (!tsk->flags & PF_EXITING) {

Annotation

Implementation Notes