linux/include/asm-generic/barrier.h
Mathieu Desnoyers fe90f3967b sched: Add missing memory barrier in switch_mm_cid
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
2024-04-16 13:59:45 +02:00

307 lines
7.4 KiB
C

/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
* Generic barrier definitions.
*
* It should be possible to use these on really simple architectures,
* but it serves more as a starting point for new ports.
*
* Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*/
#ifndef __ASM_GENERIC_BARRIER_H
#define __ASM_GENERIC_BARRIER_H
#ifndef __ASSEMBLY__
#include <linux/compiler.h>
#include <linux/kcsan-checks.h>
#include <asm/rwonce.h>
#ifndef nop
#define nop() asm volatile ("nop")
#endif
/*
* Architectures that want generic instrumentation can define __ prefixed
* variants of all barriers.
*/
#ifdef __mb
#define mb() do { kcsan_mb(); __mb(); } while (0)
#endif
#ifdef __rmb
#define rmb() do { kcsan_rmb(); __rmb(); } while (0)
#endif
#ifdef __wmb
#define wmb() do { kcsan_wmb(); __wmb(); } while (0)
#endif
#ifdef __dma_mb
#define dma_mb() do { kcsan_mb(); __dma_mb(); } while (0)
#endif
#ifdef __dma_rmb
#define dma_rmb() do { kcsan_rmb(); __dma_rmb(); } while (0)
#endif
#ifdef __dma_wmb
#define dma_wmb() do { kcsan_wmb(); __dma_wmb(); } while (0)
#endif
/*
* Force strict CPU ordering. And yes, this is required on UP too when we're
* talking to devices.
*
* Fall back to compiler barriers if nothing better is provided.
*/
#ifndef mb
#define mb() barrier()
#endif
#ifndef rmb
#define rmb() mb()
#endif
#ifndef wmb
#define wmb() mb()
#endif
#ifndef dma_mb
#define dma_mb() mb()
#endif
#ifndef dma_rmb
#define dma_rmb() rmb()
#endif
#ifndef dma_wmb
#define dma_wmb() wmb()
#endif
#ifndef __smp_mb
#define __smp_mb() mb()
#endif
#ifndef __smp_rmb
#define __smp_rmb() rmb()
#endif
#ifndef __smp_wmb
#define __smp_wmb() wmb()
#endif
#ifdef CONFIG_SMP
#ifndef smp_mb
#define smp_mb() do { kcsan_mb(); __smp_mb(); } while (0)
#endif
#ifndef smp_rmb
#define smp_rmb() do { kcsan_rmb(); __smp_rmb(); } while (0)
#endif
#ifndef smp_wmb
#define smp_wmb() do { kcsan_wmb(); __smp_wmb(); } while (0)
#endif
#else /* !CONFIG_SMP */
#ifndef smp_mb
#define smp_mb() barrier()
#endif
#ifndef smp_rmb
#define smp_rmb() barrier()
#endif
#ifndef smp_wmb
#define smp_wmb() barrier()
#endif
#endif /* CONFIG_SMP */
#ifndef __smp_store_mb
#define __smp_store_mb(var, value) do { WRITE_ONCE(var, value); __smp_mb(); } while (0)
#endif
#ifndef __smp_mb__before_atomic
#define __smp_mb__before_atomic() __smp_mb()
#endif
#ifndef __smp_mb__after_atomic
#define __smp_mb__after_atomic() __smp_mb()
#endif
#ifndef __smp_store_release
#define __smp_store_release(p, v) \
do { \
compiletime_assert_atomic_type(*p); \
__smp_mb(); \
WRITE_ONCE(*p, v); \
} while (0)
#endif
#ifndef __smp_load_acquire
#define __smp_load_acquire(p) \
({ \
__unqual_scalar_typeof(*p) ___p1 = READ_ONCE(*p); \
compiletime_assert_atomic_type(*p); \
__smp_mb(); \
(typeof(*p))___p1; \
})
#endif
#ifdef CONFIG_SMP
#ifndef smp_store_mb
#define smp_store_mb(var, value) do { kcsan_mb(); __smp_store_mb(var, value); } while (0)
#endif
#ifndef smp_mb__before_atomic
#define smp_mb__before_atomic() do { kcsan_mb(); __smp_mb__before_atomic(); } while (0)
#endif
#ifndef smp_mb__after_atomic
#define smp_mb__after_atomic() do { kcsan_mb(); __smp_mb__after_atomic(); } while (0)
#endif
#ifndef smp_store_release
#define smp_store_release(p, v) do { kcsan_release(); __smp_store_release(p, v); } while (0)
#endif
#ifndef smp_load_acquire
#define smp_load_acquire(p) __smp_load_acquire(p)
#endif
#else /* !CONFIG_SMP */
#ifndef smp_store_mb
#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); barrier(); } while (0)
#endif
#ifndef smp_mb__before_atomic
#define smp_mb__before_atomic() barrier()
#endif
#ifndef smp_mb__after_atomic
#define smp_mb__after_atomic() barrier()
#endif
#ifndef smp_store_release
#define smp_store_release(p, v) \
do { \
barrier(); \
WRITE_ONCE(*p, v); \
} while (0)
#endif
#ifndef smp_load_acquire
#define smp_load_acquire(p) \
({ \
__unqual_scalar_typeof(*p) ___p1 = READ_ONCE(*p); \
barrier(); \
(typeof(*p))___p1; \
})
#endif
#endif /* CONFIG_SMP */
/* Barriers for virtual machine guests when talking to an SMP host */
#define virt_mb() do { kcsan_mb(); __smp_mb(); } while (0)
#define virt_rmb() do { kcsan_rmb(); __smp_rmb(); } while (0)
#define virt_wmb() do { kcsan_wmb(); __smp_wmb(); } while (0)
#define virt_store_mb(var, value) do { kcsan_mb(); __smp_store_mb(var, value); } while (0)
#define virt_mb__before_atomic() do { kcsan_mb(); __smp_mb__before_atomic(); } while (0)
#define virt_mb__after_atomic() do { kcsan_mb(); __smp_mb__after_atomic(); } while (0)
#define virt_store_release(p, v) do { kcsan_release(); __smp_store_release(p, v); } while (0)
#define virt_load_acquire(p) __smp_load_acquire(p)
/**
* smp_acquire__after_ctrl_dep() - Provide ACQUIRE ordering after a control dependency
*
* A control dependency provides a LOAD->STORE order, the additional RMB
* provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order,
* aka. (load)-ACQUIRE.
*
* Architectures that do not do load speculation can have this be barrier().
*/
#ifndef smp_acquire__after_ctrl_dep
#define smp_acquire__after_ctrl_dep() smp_rmb()
#endif
/**
* smp_cond_load_relaxed() - (Spin) wait for cond with no ordering guarantees
* @ptr: pointer to the variable to wait on
* @cond: boolean expression to wait for
*
* Equivalent to using READ_ONCE() on the condition variable.
*
* Due to C lacking lambda expressions we load the value of *ptr into a
* pre-named variable @VAL to be used in @cond.
*/
#ifndef smp_cond_load_relaxed
#define smp_cond_load_relaxed(ptr, cond_expr) ({ \
typeof(ptr) __PTR = (ptr); \
__unqual_scalar_typeof(*ptr) VAL; \
for (;;) { \
VAL = READ_ONCE(*__PTR); \
if (cond_expr) \
break; \
cpu_relax(); \
} \
(typeof(*ptr))VAL; \
})
#endif
/**
* smp_cond_load_acquire() - (Spin) wait for cond with ACQUIRE ordering
* @ptr: pointer to the variable to wait on
* @cond: boolean expression to wait for
*
* Equivalent to using smp_load_acquire() on the condition variable but employs
* the control dependency of the wait to reduce the barrier on many platforms.
*/
#ifndef smp_cond_load_acquire
#define smp_cond_load_acquire(ptr, cond_expr) ({ \
__unqual_scalar_typeof(*ptr) _val; \
_val = smp_cond_load_relaxed(ptr, cond_expr); \
smp_acquire__after_ctrl_dep(); \
(typeof(*ptr))_val; \
})
#endif
/*
* pmem_wmb() ensures that all stores for which the modification
* are written to persistent storage by preceding instructions have
* updated persistent storage before any data access or data transfer
* caused by subsequent instructions is initiated.
*/
#ifndef pmem_wmb
#define pmem_wmb() wmb()
#endif
/*
* ioremap_wc() maps I/O memory as memory with write-combining attributes. For
* this kind of memory accesses, the CPU may wait for prior accesses to be
* merged with subsequent ones. In some situation, such wait is bad for the
* performance. io_stop_wc() can be used to prevent the merging of
* write-combining memory accesses before this macro with those after it.
*/
#ifndef io_stop_wc
#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 */