Commit 3b680865 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'sched_urgent_for_v6.9_rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull scheduler fix from Borislav Petkov:

 - Add a missing memory barrier in the concurrency ID mm switching

* tag 'sched_urgent_for_v6.9_rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched: Add missing memory barrier in switch_mm_cid
parents d07a0b86 fe90f396

arch/x86/include/asm/barrier.h

+3 −0
Original line number Diff line number Diff line
@@ -79,6 +79,9 @@ do { \ 
#define __smp_mb__before_atomic()	do { } while (0)

#define __smp_mb__after_atomic()	do { } while (0)



/* Writing to CR3 provides a full memory barrier in switch_mm(). */

#define smp_mb__after_switch_mm()	do { } while (0)



#include <asm-generic/barrier.h>



#endif /* _ASM_X86_BARRIER_H */

include/asm-generic/barrier.h

+8 −0
Original line number Diff line number Diff line
@@ -294,5 +294,13 @@ do { \ 
#define io_stop_wc() do { } while (0)

#endif



/*

 * Architectures that guarantee an implicit smp_mb() in switch_mm()

 * can override smp_mb__after_switch_mm.

 */

#ifndef smp_mb__after_switch_mm

# define smp_mb__after_switch_mm()	smp_mb()

#endif



#endif /* !__ASSEMBLY__ */

#endif /* __ASM_GENERIC_BARRIER_H */

kernel/sched/sched.h

+14 −6
Original line number Diff line number Diff line
@@ -79,6 +79,8 @@ 
# include <asm/paravirt_api_clock.h>

#endif



#include <asm/barrier.h>



#include "cpupri.h"

#include "cpudeadline.h"
@@ -3445,13 +3447,19 @@ static inline void switch_mm_cid(struct rq *rq, 
		 * between rq->curr store and load of {prev,next}->mm->pcpu_cid[cpu].

		 * Provide it here.

		 */

		if (!prev->mm)                          // from kernel

		if (!prev->mm) {                        // from kernel

			smp_mb();

		} else {				// from user

			/*

		 * user -> user transition guarantees a memory barrier through

		 * switch_mm() when current->mm changes. If current->mm is

		 * unchanged, no barrier is needed.

			 * user->user transition relies on an implicit

			 * memory barrier in switch_mm() when

			 * current->mm changes. If the architecture

			 * switch_mm() does not have an implicit memory

			 * barrier, it is emitted here.  If current->mm

			 * is unchanged, no barrier is needed.

			 */

			smp_mb__after_switch_mm();

		}

	}

	if (prev->mm_cid_active) {

		mm_cid_snapshot_time(rq, prev->mm);