lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Mon, 9 Jun 2014 20:45:14 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: Thomas Gleixner <tglx@...utronix.de> Cc: LKML <linux-kernel@...r.kernel.org>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, Lai Jiangshan <laijs@...fujitsu.com>, Jason Low <jason.low2@...com>, Brad Mouring <bmouring@...com> Subject: Re: [patch V3 3/7] rtmutex: Document pi chain walk On Mon, 09 Jun 2014 20:28:08 -0000 Thomas Gleixner <tglx@...utronix.de> wrote: > Add commentry to document the chain walk and the protection mechanisms > and their scope. > > Signed-off-by: Thomas Gleixner <tglx@...utronix.de> > --- > kernel/locking/rtmutex.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 52 insertions(+) > > Index: tip/kernel/locking/rtmutex.c > =================================================================== > --- tip.orig/kernel/locking/rtmutex.c > +++ tip/kernel/locking/rtmutex.c > @@ -285,6 +285,47 @@ static inline struct rt_mutex *task_bloc > * @top_task: the current top waiter > * > * Returns 0 or -EDEADLK. > + * > + * Chain walk basics and protection scope > + * > + * [A] refcount on task > + * [B] task->pi_lock held > + * [C] rtmutex->lock held A,B, C is rather meaningless, and requires constant looking back up at the key. Perhaps [R],[P] and [L] [R] refcount on task (get_task_struct) [P] task->pi_lock held [L] rtmutex->lock held That way we can associate R being refcount, P being pi_lock and L being lock. Easier to remember. > + * > + * call() Protected by "call()"? > + * @task [A] > + * @orig_lock if != NULL @top_task is blocked on it > + * @next_lock Unprotected. Cannot be > + * dereferenced. Only used for > + * comparison. > + * @orig_waiter if != NULL @top_task is blocked on it > + * @top_task current, or in case of proxy > + * locking protected by calling > + * code > + * again: > + * loop_sanity_check(); > + * retry: > + * lock(task->pi_lock); [A] acquire [B] > + * waiter = task->pi_blocked_on; [B] > + * check_exit_conditions(); [B] > + * lock = waiter->lock; [B] > + * if (!try_lock(lock->wait_lock)) { [B] try to acquire [C] > + * unlock(task->pi_lock); drop [B] > + * goto retry; > + * } > + * check_exit_conditions(); [B] + [C] > + * requeue_lock_waiter(lock, waiter); [B] + [C] > + * unlock(task->pi_lock); drop [B] > + * drop_task_ref(task); drop [A] Maybe just state "put_task_struct()", less abstractions. > + * check_exit_conditions(); [C] > + * task = owner(lock); [C] > + * get_task_ref(task); [C] acquire [A] get_task_struct() -- Steve > + * lock(task->pi_lock); [C] acquire [B] > + * requeue_pi_waiter(task, waiters(lock)); [B] + [C] > + * check_exit_conditions(); [B] + [C] > + * unlock(task->pi_lock); drop [B] > + * unlock(lock->wait_lock); drop [C] > + * goto again; > */ > static int rt_mutex_adjust_prio_chain(struct task_struct *task, > int deadlock_detect, > @@ -326,6 +367,12 @@ static int rt_mutex_adjust_prio_chain(st > > return -EDEADLK; > } > + > + /* > + * We are fully preemptible here and only hold the refcount on > + * @task. So everything can have changed under us since the > + * caller or our own code below (goto retry) dropped all locks. > + */ > retry: > /* > * Task can not go away as we did a get_task() before ! > @@ -383,6 +430,11 @@ static int rt_mutex_adjust_prio_chain(st > if (!detect_deadlock && waiter->prio == task->prio) > goto out_unlock_pi; > > + /* > + * We need to trylock here as we are holding task->pi_lock, > + * which is the reverse lock order versus the other rtmutex > + * operations. > + */ > lock = waiter->lock; > if (!raw_spin_trylock(&lock->wait_lock)) { > raw_spin_unlock_irqrestore(&task->pi_lock, flags); > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists