Commit cec1e6e5 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'sched_ext-for-6.17-rc7-fixes' of... 

Merge tag 'sched_ext-for-6.17-rc7-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext

Pull sched_ext fix from jun Heo:
 "This contains a fix for sched_ext idle CPU selection that likely fixes
  a substantial performance regression.

  The scx_bpf_select_cpu_dfl/and() kfuncs were incorrectly detecting all
  tasks as migration-disabled when called outside ops.select_cpu(),
  causing them to always return -EBUSY instead of finding idle CPUs.

  The fix properly distinguishes between genuinely migration-disabled
  tasks vs. the current task whose migration is temporarily disabled by
  BPF execution"

* tag 'sched_ext-for-6.17-rc7-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext:
  sched_ext: idle: Handle migration-disabled tasks in BPF code
parents d4c7fccf 55ed11b1

kernel/sched/ext_idle.c

+27 −1
Original line number Diff line number Diff line
@@ -856,6 +856,32 @@ static bool check_builtin_idle_enabled(void) 
	return false;

}



/*

 * Determine whether @p is a migration-disabled task in the context of BPF

 * code.

 *

 * We can't simply check whether @p->migration_disabled is set in a

 * sched_ext callback, because migration is always disabled for the current

 * task while running BPF code.

 *

 * The prolog (__bpf_prog_enter) and epilog (__bpf_prog_exit) respectively

 * disable and re-enable migration. For this reason, the current task

 * inside a sched_ext callback is always a migration-disabled task.

 *

 * Therefore, when @p->migration_disabled == 1, check whether @p is the

 * current task or not: if it is, then migration was not disabled before

 * entering the callback, otherwise migration was disabled.

 *

 * Returns true if @p is migration-disabled, false otherwise.

 */

static bool is_bpf_migration_disabled(const struct task_struct *p)

{

	if (p->migration_disabled == 1)

		return p != current;

	else

		return p->migration_disabled;

}



static s32 select_cpu_from_kfunc(struct task_struct *p, s32 prev_cpu, u64 wake_flags,

				 const struct cpumask *allowed, u64 flags)

{
@@ -898,7 +924,7 @@ static s32 select_cpu_from_kfunc(struct task_struct *p, s32 prev_cpu, u64 wake_f 
	 * selection optimizations and simply check whether the previously

	 * used CPU is idle and within the allowed cpumask.

	 */

	if (p->nr_cpus_allowed == 1 || is_migration_disabled(p)) {

	if (p->nr_cpus_allowed == 1 || is_bpf_migration_disabled(p)) {

		if (cpumask_test_cpu(prev_cpu, allowed ?: p->cpus_ptr) &&

		    scx_idle_test_and_clear_cpu(prev_cpu))

			cpu = prev_cpu;