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Many architectures' switch_mm() (e.g. arm64) do not have an smp_mb()
which the core scheduler code has depended upon since commit:
commit 223baf9d17 ("sched: Fix performance regression introduced by mm_cid")
If switch_mm() doesn't call smp_mb(), sched_mm_cid_remote_clear() can
unset the actively used cid when it fails to observe active task after it
sets lazy_put.
There *is* a memory barrier between storing to rq->curr and _return to
userspace_ (as required by membarrier), but the rseq mm_cid has stricter
requirements: the barrier needs to be issued between store to rq->curr
and switch_mm_cid(), which happens earlier than:
- spin_unlock(),
- switch_to().
So it's fine when the architecture switch_mm() happens to have that
barrier already, but less so when the architecture only provides the
full barrier in switch_to() or spin_unlock().
It is a bug in the rseq switch_mm_cid() implementation. All architectures
that don't have memory barriers in switch_mm(), but rather have the full
barrier either in finish_lock_switch() or switch_to() have them too late
for the needs of switch_mm_cid().
Introduce a new smp_mb__after_switch_mm(), defined as smp_mb() in the
generic barrier.h header, and use it in switch_mm_cid() for scheduler
transitions where switch_mm() is expected to provide a memory barrier.
Architectures can override smp_mb__after_switch_mm() if their
switch_mm() implementation provides an implicit memory barrier.
Override it with a no-op on x86 which implicitly provide this memory
barrier by writing to CR3.
Fixes: 223baf9d17 ("sched: Fix performance regression introduced by mm_cid")
Reported-by: levi.yun <yeoreum.yun@arm.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> # for arm64
Acked-by: Dave Hansen <dave.hansen@linux.intel.com> # for x86
Cc: <stable@vger.kernel.org> # 6.4.x
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20240415152114.59122-2-mathieu.desnoyers@efficios.com
307 lines
7.4 KiB
C
307 lines
7.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
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/*
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* Generic barrier definitions.
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*
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* It should be possible to use these on really simple architectures,
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* but it serves more as a starting point for new ports.
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*
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* Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*/
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#ifndef __ASM_GENERIC_BARRIER_H
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#define __ASM_GENERIC_BARRIER_H
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#ifndef __ASSEMBLY__
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#include <linux/compiler.h>
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#include <linux/kcsan-checks.h>
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#include <asm/rwonce.h>
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#ifndef nop
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#define nop() asm volatile ("nop")
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#endif
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/*
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* Architectures that want generic instrumentation can define __ prefixed
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* variants of all barriers.
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*/
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#ifdef __mb
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#define mb() do { kcsan_mb(); __mb(); } while (0)
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#endif
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#ifdef __rmb
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#define rmb() do { kcsan_rmb(); __rmb(); } while (0)
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#endif
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#ifdef __wmb
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#define wmb() do { kcsan_wmb(); __wmb(); } while (0)
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#endif
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#ifdef __dma_mb
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#define dma_mb() do { kcsan_mb(); __dma_mb(); } while (0)
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#endif
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#ifdef __dma_rmb
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#define dma_rmb() do { kcsan_rmb(); __dma_rmb(); } while (0)
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#endif
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#ifdef __dma_wmb
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#define dma_wmb() do { kcsan_wmb(); __dma_wmb(); } while (0)
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#endif
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/*
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* Force strict CPU ordering. And yes, this is required on UP too when we're
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* talking to devices.
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*
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* Fall back to compiler barriers if nothing better is provided.
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*/
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#ifndef mb
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#define mb() barrier()
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#endif
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#ifndef rmb
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#define rmb() mb()
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#endif
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#ifndef wmb
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#define wmb() mb()
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#endif
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#ifndef dma_mb
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#define dma_mb() mb()
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#endif
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#ifndef dma_rmb
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#define dma_rmb() rmb()
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#endif
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#ifndef dma_wmb
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#define dma_wmb() wmb()
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#endif
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#ifndef __smp_mb
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#define __smp_mb() mb()
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#endif
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#ifndef __smp_rmb
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#define __smp_rmb() rmb()
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#endif
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#ifndef __smp_wmb
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#define __smp_wmb() wmb()
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#endif
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#ifdef CONFIG_SMP
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#ifndef smp_mb
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#define smp_mb() do { kcsan_mb(); __smp_mb(); } while (0)
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#endif
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#ifndef smp_rmb
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#define smp_rmb() do { kcsan_rmb(); __smp_rmb(); } while (0)
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#endif
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#ifndef smp_wmb
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#define smp_wmb() do { kcsan_wmb(); __smp_wmb(); } while (0)
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#endif
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#else /* !CONFIG_SMP */
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#ifndef smp_mb
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#define smp_mb() barrier()
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#endif
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#ifndef smp_rmb
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#define smp_rmb() barrier()
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#endif
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#ifndef smp_wmb
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#define smp_wmb() barrier()
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#endif
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#endif /* CONFIG_SMP */
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#ifndef __smp_store_mb
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#define __smp_store_mb(var, value) do { WRITE_ONCE(var, value); __smp_mb(); } while (0)
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#endif
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#ifndef __smp_mb__before_atomic
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#define __smp_mb__before_atomic() __smp_mb()
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#endif
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#ifndef __smp_mb__after_atomic
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#define __smp_mb__after_atomic() __smp_mb()
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#endif
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#ifndef __smp_store_release
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#define __smp_store_release(p, v) \
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do { \
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compiletime_assert_atomic_type(*p); \
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__smp_mb(); \
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WRITE_ONCE(*p, v); \
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} while (0)
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#endif
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#ifndef __smp_load_acquire
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#define __smp_load_acquire(p) \
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({ \
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__unqual_scalar_typeof(*p) ___p1 = READ_ONCE(*p); \
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compiletime_assert_atomic_type(*p); \
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__smp_mb(); \
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(typeof(*p))___p1; \
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})
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#endif
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#ifdef CONFIG_SMP
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#ifndef smp_store_mb
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#define smp_store_mb(var, value) do { kcsan_mb(); __smp_store_mb(var, value); } while (0)
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#endif
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#ifndef smp_mb__before_atomic
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#define smp_mb__before_atomic() do { kcsan_mb(); __smp_mb__before_atomic(); } while (0)
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#endif
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#ifndef smp_mb__after_atomic
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#define smp_mb__after_atomic() do { kcsan_mb(); __smp_mb__after_atomic(); } while (0)
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#endif
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#ifndef smp_store_release
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#define smp_store_release(p, v) do { kcsan_release(); __smp_store_release(p, v); } while (0)
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#endif
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#ifndef smp_load_acquire
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#define smp_load_acquire(p) __smp_load_acquire(p)
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#endif
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#else /* !CONFIG_SMP */
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#ifndef smp_store_mb
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#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); barrier(); } while (0)
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#endif
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#ifndef smp_mb__before_atomic
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#define smp_mb__before_atomic() barrier()
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#endif
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#ifndef smp_mb__after_atomic
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#define smp_mb__after_atomic() barrier()
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#endif
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#ifndef smp_store_release
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#define smp_store_release(p, v) \
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do { \
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barrier(); \
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WRITE_ONCE(*p, v); \
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} while (0)
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#endif
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#ifndef smp_load_acquire
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#define smp_load_acquire(p) \
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({ \
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__unqual_scalar_typeof(*p) ___p1 = READ_ONCE(*p); \
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barrier(); \
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(typeof(*p))___p1; \
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})
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#endif
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#endif /* CONFIG_SMP */
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/* Barriers for virtual machine guests when talking to an SMP host */
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#define virt_mb() do { kcsan_mb(); __smp_mb(); } while (0)
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#define virt_rmb() do { kcsan_rmb(); __smp_rmb(); } while (0)
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#define virt_wmb() do { kcsan_wmb(); __smp_wmb(); } while (0)
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#define virt_store_mb(var, value) do { kcsan_mb(); __smp_store_mb(var, value); } while (0)
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#define virt_mb__before_atomic() do { kcsan_mb(); __smp_mb__before_atomic(); } while (0)
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#define virt_mb__after_atomic() do { kcsan_mb(); __smp_mb__after_atomic(); } while (0)
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#define virt_store_release(p, v) do { kcsan_release(); __smp_store_release(p, v); } while (0)
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#define virt_load_acquire(p) __smp_load_acquire(p)
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/**
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* smp_acquire__after_ctrl_dep() - Provide ACQUIRE ordering after a control dependency
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*
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* A control dependency provides a LOAD->STORE order, the additional RMB
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* provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order,
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* aka. (load)-ACQUIRE.
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*
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* Architectures that do not do load speculation can have this be barrier().
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*/
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#ifndef smp_acquire__after_ctrl_dep
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#define smp_acquire__after_ctrl_dep() smp_rmb()
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#endif
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/**
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* smp_cond_load_relaxed() - (Spin) wait for cond with no ordering guarantees
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* @ptr: pointer to the variable to wait on
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* @cond: boolean expression to wait for
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*
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* Equivalent to using READ_ONCE() on the condition variable.
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*
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* Due to C lacking lambda expressions we load the value of *ptr into a
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* pre-named variable @VAL to be used in @cond.
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*/
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#ifndef smp_cond_load_relaxed
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#define smp_cond_load_relaxed(ptr, cond_expr) ({ \
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typeof(ptr) __PTR = (ptr); \
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__unqual_scalar_typeof(*ptr) VAL; \
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for (;;) { \
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VAL = READ_ONCE(*__PTR); \
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if (cond_expr) \
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break; \
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cpu_relax(); \
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} \
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(typeof(*ptr))VAL; \
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})
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#endif
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/**
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* smp_cond_load_acquire() - (Spin) wait for cond with ACQUIRE ordering
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* @ptr: pointer to the variable to wait on
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* @cond: boolean expression to wait for
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*
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* Equivalent to using smp_load_acquire() on the condition variable but employs
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* the control dependency of the wait to reduce the barrier on many platforms.
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*/
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#ifndef smp_cond_load_acquire
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#define smp_cond_load_acquire(ptr, cond_expr) ({ \
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__unqual_scalar_typeof(*ptr) _val; \
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_val = smp_cond_load_relaxed(ptr, cond_expr); \
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smp_acquire__after_ctrl_dep(); \
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(typeof(*ptr))_val; \
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})
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#endif
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/*
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* pmem_wmb() ensures that all stores for which the modification
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* are written to persistent storage by preceding instructions have
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* updated persistent storage before any data access or data transfer
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* caused by subsequent instructions is initiated.
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*/
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#ifndef pmem_wmb
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#define pmem_wmb() wmb()
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#endif
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/*
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* ioremap_wc() maps I/O memory as memory with write-combining attributes. For
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* this kind of memory accesses, the CPU may wait for prior accesses to be
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* merged with subsequent ones. In some situation, such wait is bad for the
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* performance. io_stop_wc() can be used to prevent the merging of
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* write-combining memory accesses before this macro with those after it.
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*/
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#ifndef io_stop_wc
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#define io_stop_wc() do { } while (0)
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#endif
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/*
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* Architectures that guarantee an implicit smp_mb() in switch_mm()
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* can override smp_mb__after_switch_mm.
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*/
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#ifndef smp_mb__after_switch_mm
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# define smp_mb__after_switch_mm() smp_mb()
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#endif
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#endif /* !__ASSEMBLY__ */
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#endif /* __ASM_GENERIC_BARRIER_H */
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