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schedlock 3/4

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Eliminate lock recursion from turnstiles.  This was simply used to avoid
tracking the top-level turnstile lock.  explicitly check for it before
picking up and dropping locks.

Reviewed by:	kib
Tested by:	pho
Differential Revision:	https://reviews.freebsd.org/D22746
This commit is contained in:
Jeff Roberson 2019-12-15 21:19:41 +00:00
parent 045b7c6084
commit 1c81a87efd
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=355782
1 changed files with 36 additions and 14 deletions
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50
sys/kern/subr_turnstile.c
View file

@ -175,6 +175,22 @@ SDT_PROBE_DEFINE(sched, , , sleep);
SDT_PROBE_DEFINE2(sched, , , wakeup, "struct thread *",
"struct proc *");
static inline void
propagate_unlock_ts(struct turnstile *top, struct turnstile *ts)
{
if (ts != top)
mtx_unlock_spin(&ts->ts_lock);
}
static inline void
propagate_unlock_td(struct turnstile *top, struct thread *td)
{
if (td->td_lock != &top->ts_lock)
thread_unlock(td);
}
/*
* Walks the chain of turnstiles and their owners to propagate the priority
* of the thread being blocked to all the threads holding locks that have to
@ -183,20 +199,19 @@ SDT_PROBE_DEFINE2(sched, , , wakeup, "struct thread *",
static void
propagate_priority(struct thread *td)
{
struct turnstile *ts;
struct turnstile *ts, *top;
int pri;
THREAD_LOCK_ASSERT(td, MA_OWNED);
pri = td->td_priority;
ts = td->td_blocked;
top = ts = td->td_blocked;
THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock);
/*
* Grab a recursive lock on this turnstile chain so it stays locked
* for the whole operation. The caller expects us to return with
* the original lock held. We only ever lock down the chain so
* the lock order is constant.
* The original turnstile lock is held across the entire
* operation. We only ever lock down the chain so the lock
* order is constant.
*/
mtx_lock_spin(&ts->ts_lock);
for (;;) {
td = ts->ts_owner;
@ -205,12 +220,19 @@ propagate_priority(struct thread *td)
* This might be a read lock with no owner. There's
* not much we can do, so just bail.
*/
mtx_unlock_spin(&ts->ts_lock);
propagate_unlock_ts(top, ts);
return;
}
thread_lock_flags(td, MTX_DUPOK);
mtx_unlock_spin(&ts->ts_lock);
/*
* Wait for the thread lock to be stable and then only
* acquire if it is not the turnstile lock.
*/
thread_lock_block_wait(td);
if (td->td_lock != &ts->ts_lock) {
thread_lock_flags(td, MTX_DUPOK);
propagate_unlock_ts(top, ts);
}
MPASS(td->td_proc != NULL);
MPASS(td->td_proc->p_magic == P_MAGIC);
@ -233,7 +255,7 @@ propagate_priority(struct thread *td)
* thread that is being blocked, we are finished.
*/
if (td->td_priority <= pri) {
thread_unlock(td);
propagate_unlock_td(top, td);
return;
}
@ -248,7 +270,7 @@ propagate_priority(struct thread *td)
*/
if (TD_IS_RUNNING(td) || TD_ON_RUNQ(td)) {
MPASS(td->td_blocked == NULL);
thread_unlock(td);
propagate_unlock_td(top, td);
return;
}
@ -276,7 +298,7 @@ propagate_priority(struct thread *td)
THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock);
/* Resort td on the list if needed. */
if (!turnstile_adjust_thread(ts, td)) {
mtx_unlock_spin(&ts->ts_lock);
propagate_unlock_ts(top, ts);
return;
}
/* The thread lock is released as ts lock above. */
@ -498,7 +520,7 @@ turnstile_init(void *mem, int size, int flags)
TAILQ_INIT(&ts->ts_blocked[TS_SHARED_QUEUE]);
TAILQ_INIT(&ts->ts_pending);
LIST_INIT(&ts->ts_free);
mtx_init(&ts->ts_lock, "turnstile lock", NULL, MTX_SPIN | MTX_RECURSE);
mtx_init(&ts->ts_lock, "turnstile lock", NULL, MTX_SPIN);
return (0);
}