archives/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-03-08 01:04:41 +01:00
Code Issues Projects Releases Packages Wiki Activity Actions

sched/debug: Fix dl_server (re)start conditions

Browse source 
There are two problems with sched_server_write_common() that can cause the
dl_server to malfunction upon attempting to change the parameters:

1) when, after having disabled the dl_server by setting runtime=0, it is
   enabled again while tasks are already enqueued. In this case is_active would
   still be 0 and dl_server_start() would not be called.

2) when dl_server_apply_params() would fail, runtime is not applied and does
   not reflect the new state.

Instead have dl_server_start() check its actual dl_runtime, and have
sched_server_write_common() unconditionally (re)start the dl_server. It will
automatically stop if there isn't anything to do, so spurious activation is
harmless -- while failing to start it is a problem.

While there, move the printk out of the locked region and make it symmetric,
also printing on enable.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260203103407.GK1282955@noisy.programming.kicks-ass.net
This commit is contained in:
Peter Zijlstra 2026-02-03 11:05:12 +01:00
parent 76d12132ba
commit 5a40a9bb56
2 changed files with 16 additions and 21 deletions
Download patch file Download diff file Expand all files Collapse all files

5
kernel/sched/deadline.c
View file

@ -1799,7 +1799,7 @@ void dl_server_start(struct sched_dl_entity *dl_se)
struct rq *rq = dl_se->rq;
dl_se->dl_defer_idle = 0;
if (!dl_server(dl_se) || dl_se->dl_server_active)
if (!dl_server(dl_se) || dl_se->dl_server_active || !dl_se->dl_runtime)
return;
/*
@ -1898,7 +1898,6 @@ int dl_server_apply_params(struct sched_dl_entity *dl_se, u64 runtime, u64 perio
int cpu = cpu_of(rq);
struct dl_bw *dl_b;
unsigned long cap;
int retval = 0;
int cpus;
dl_b = dl_bw_of(cpu);
@ -1930,7 +1929,7 @@ int dl_server_apply_params(struct sched_dl_entity *dl_se, u64 runtime, u64 perio
dl_se->dl_bw = to_ratio(dl_se->dl_period, dl_se->dl_runtime);
dl_se->dl_density = to_ratio(dl_se->dl_deadline, dl_se->dl_runtime);
return retval;
return 0;
}
/*

32
kernel/sched/debug.c
View file

@ -338,9 +338,9 @@ static ssize_t sched_server_write_common(struct file *filp, const char __user *u
void *server)
{
long cpu = (long) ((struct seq_file *) filp->private_data)->private;
struct rq *rq = cpu_rq(cpu);
struct sched_dl_entity *dl_se = (struct sched_dl_entity *)server;
u64 runtime, period;
u64 old_runtime, runtime, period;
struct rq *rq = cpu_rq(cpu);
int retval = 0;
size_t err;
u64 value;
@ -350,9 +350,7 @@ static ssize_t sched_server_write_common(struct file *filp, const char __user *u
return err;
scoped_guard (rq_lock_irqsave, rq) {
bool is_active;
runtime = dl_se->dl_runtime;
old_runtime = runtime = dl_se->dl_runtime;
period = dl_se->dl_period;
switch (param) {
@ -374,25 +372,23 @@ static ssize_t sched_server_write_common(struct file *filp, const char __user *u
return -EINVAL;
}
is_active = dl_server_active(dl_se);
if (is_active) {
update_rq_clock(rq);
dl_server_stop(dl_se);
}
update_rq_clock(rq);
dl_server_stop(dl_se);
retval = dl_server_apply_params(dl_se, runtime, period, 0);
if (!runtime)
printk_deferred("%s server disabled in CPU %d, system may crash due to starvation.\n",
server == &rq->fair_server ? "Fair" : "Ext", cpu_of(rq));
if (is_active && runtime)
dl_server_start(dl_se);
dl_server_start(dl_se);
if (retval < 0)
return retval;
}
if (!!old_runtime ^ !!runtime) {
pr_info("%s server %sabled on CPU %d%s.\n",
server == &rq->fair_server ? "Fair" : "Ext",
runtime ? "en" : "dis",
cpu_of(rq),
runtime ? "" : ", system may malfunction due to starvation");
}
*ppos += cnt;
return cnt;
}