github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-07-28 10:09:10 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

sched: Add is_blocked task flag

Browse Source 
Add a new is_blocked flag to the task struct. This flag is set
by try_to_block_task() and cleared by ttwu_do_wakeup() and
tracks if the task is blocked.

Traditionally this would mirror !p->on_rq, however due things
like DELAY_DEQUEUE and PROXY_EXEC, this can diverge, so its
useful to manage separately.

Additionally with this, we might be able to get rid of the
p->se.sched_delayed (ab)use in the core code (eventually).

Taken whole cloth from Peter's email:
  https://lore.kernel.org/lkml/20260501132143.GC1026330@noisy.programming.kicks-ass.net/

With a few additional p->is_blocked = 0 in a few cases where
we return current if blocked_on gets zeroed or there is
no owner. This may hint that these current special cases
might be dropped eventually.

This change also helps resolve wait-queue stalls seen with
proxy-execution. See previous patch attempts for details:
  https://lore.kernel.org/lkml/20260430215103.2978955-2-jstultz@google.com/

Reported-by: Vineeth Pillai <vineethrp@google.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260512025635.2840817-7-jstultz@google.com
This commit is contained in:
John Stultz 2026-05-12 02:56:16 +00:00 committed by Peter Zijlstra
parent f13beb010e
commit 4c2a20413d
2 changed files with 20 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
include/linux/sched.h
View File

@ -852,7 +852,11 @@ struct task_struct {
struct alloc_tag *alloc_tag;
#endif
int on_cpu;
u8 on_cpu;
u8 on_rq;
u8 is_blocked;
u8 __pad;
struct __call_single_node wake_entry;
unsigned int wakee_flips;
unsigned long wakee_flip_decay_ts;
@ -867,7 +871,6 @@ struct task_struct {
*/
int recent_used_cpu;
int wake_cpu;
int on_rq;
int prio;
int static_prio;

16
kernel/sched/core.c
View File

@ -624,6 +624,12 @@ int task_llc(const struct task_struct *p)
* [ The astute reader will observe that it is possible for two tasks on one
* CPU to have ->on_cpu = 1 at the same time. ]
*
* p->is_blocked <- { 0, 1 }:
*
* is set by try_to_block_task() and cleared by ttwu_do_wakeup() and tracks
* if the task is blocked. Traditionally this would mirror p->on_rq, however
* due things like DELAY_DEQUEUE and PROXY_EXEC, this can diverge.
*
* task_cpu(p): is changed by set_task_cpu(), the rules are:
*
* - Don't call set_task_cpu() on a blocked task:
@ -3719,6 +3725,7 @@ ttwu_stat(struct task_struct *p, int cpu, int wake_flags)
*/
static inline void ttwu_do_wakeup(struct task_struct *p)
{
p->is_blocked = 0;
WRITE_ONCE(p->__state, TASK_RUNNING);
trace_sched_wakeup(p);
}
@ -4252,6 +4259,7 @@ int try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
* it disabling IRQs (this allows not taking ->pi_lock).
*/
WARN_ON_ONCE(p->se.sched_delayed);
WARN_ON_ONCE(p->is_blocked);
/* If p is current, we know we can run here, so clear blocked_on */
clear_task_blocked_on(p, NULL);
if (!ttwu_state_match(p, state, &success))
@ -4563,6 +4571,7 @@ static void __sched_fork(u64 clone_flags, struct task_struct *p)
/* A delayed task cannot be in clone(). */
WARN_ON_ONCE(p->se.sched_delayed);
WARN_ON_ONCE(p->is_blocked);
#ifdef CONFIG_FAIR_GROUP_SCHED
p->se.cfs_rq = NULL;
@ -6676,6 +6685,7 @@ static bool try_to_block_task(struct rq *rq, struct task_struct *p,
unsigned long task_state = *task_state_p;
if (signal_pending_state(task_state, p)) {
p->is_blocked = 0;
WRITE_ONCE(p->__state, TASK_RUNNING);
*task_state_p = TASK_RUNNING;
clear_task_blocked_on(p, NULL);
@ -6683,6 +6693,8 @@ static bool try_to_block_task(struct rq *rq, struct task_struct *p,
return false;
}
p->is_blocked = 1;
/*
* We check should_block after signal_pending because we
* will want to wake the task in that case. But if
@ -6843,6 +6855,7 @@ find_proxy_task(struct rq *rq, struct task_struct *donor, struct rq_flags *rf)
/* if its PROXY_WAKING, do return migration or run if current */
if (mutex == PROXY_WAKING) {
if (task_current(rq, p)) {
p->is_blocked = 0;
clear_task_blocked_on(p, PROXY_WAKING);
return p;
}
@ -6878,6 +6891,7 @@ find_proxy_task(struct rq *rq, struct task_struct *donor, struct rq_flags *rf)
* just run on this rq), or return-migrate the task.
*/
if (task_current(rq, p)) {
p->is_blocked = 0;
__clear_task_blocked_on(p, NULL);
return p;
}
@ -7111,7 +7125,7 @@ static void __sched notrace __schedule(int sched_mode)
clear_task_blocked_on(prev, NULL);
rq_set_donor(rq, next);
if (unlikely(next->blocked_on)) {
if (unlikely(next->is_blocked && next->blocked_on)) {
next = find_proxy_task(rq, next, &rf);
if (!next) {
zap_balance_callbacks(rq);