On Tue, Mar 05, 2024 at 02:53:35PM +0000, levi.yun wrote:
Currently arm64's switch_mm() doesn't always have an smp_mb() which the core scheduler code has depended upon since commit:
commit 223baf9d17f25 ("sched: Fix performance regression introduced by mm_cid")If switch_mm() doesn't call smp_mb(), sched_mm_cid_remote_clear() can unset the activly used cid when it fails to observe active task after it sets lazy_put.
By adding an smp_mb() in arm64's check_and_switch_context(), Guarantee to observe active task after sched_mm_cid_remote_clear() success to set lazy_put.
Signed-off-by: levi.yun yeoreum.yun@arm.com Fixes: 223baf9d17f2 ("sched: Fix performance regression introduced by mm_cid") Cc: stable@vger.kernel.org # 6.4.x Cc: Mathieu Desnoyers mathieu.desnoyers@efficios.com Cc: Catalin Marinas catalin.marinas@arm.com Cc: Mark Rutland mark.rutland@arm.com Cc: Will Deacon will@kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: Aaron Lu aaron.lu@intel.com
I'm really sorry if you got this multiple times. I had some problems with the SMTP server...
arch/arm64/mm/context.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c index 188197590fc9..7a9e8e6647a0 100644 --- a/arch/arm64/mm/context.c +++ b/arch/arm64/mm/context.c @@ -268,6 +268,11 @@ void check_and_switch_context(struct mm_struct *mm) */ if (!system_uses_ttbr0_pan()) cpu_switch_mm(mm->pgd, mm);
- /*
* See the comments on switch_mm_cid describing user -> user transition.*/- smp_mb();
}
We already have a stronger barrier than smp_mb() (dsb ish) in __switch_to(). Is that not sufficient?
Will