Peter Zijlstra wrote:
Oleg wrote:
"Historically ->signal/->sighand (both ptrs and their contents) were globally
protected by tasklist_lock. 'current' can use these pointers lockless, they
can't be changed under him.
Nowadays ->signal/->sighand are _also_ protected by ->sighand->siglock.
Unless you are current, you can't lock ->siglock directly (without holding
tasklist_lock), you should use lock_task_sighand()."
Then, to be consistent with the rest of the kernel, ->signal->tty
locking should look like so:
mutex_lock(&tty_mutex)
read_lock(&tasklist_lock)
lock_task_sighand(p, &flags)
It would be nice if we could clean up some of the complicated locking in
this code. For example, from do_tty_hangup,
*
* Locking:
* BKL
* redirect lock for undoing redirection
* file list lock for manipulating list of ttys
* tty_ldisc_lock from called functions
* termios_sem resetting termios data
* tasklist_lock to walk task list for hangup event
P.
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