membarrier: Explicitly sync remote cores when SYNC_CORE is requested

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membarrier() does not explicitly sync_core() remote CPUs; instead, it
relies on the assumption that an IPI will result in a core sync.  On x86,
this may be true in practice, but it's not architecturally reliable.  In
particular, the SDM and APM do not appear to guarantee that interrupt
delivery is serializing.  While IRET does serialize, IPI return can
schedule, thereby switching to another task in the same mm that was
sleeping in a syscall.  The new task could then SYSRET back to usermode
without ever executing IRET.

Make this more robust by explicitly calling sync_core_before_usermode()
on remote cores.  (This also helps people who search the kernel tree for
instances of sync_core() and sync_core_before_usermode() -- one might be
surprised that the core membarrier code doesn't currently show up in a
such a search.)

Fixes: 70216e18e5 ("membarrier: Provide core serializing command, *_SYNC_CORE")
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/776b448d5f7bd6b12690707f5ed67bcda7f1d427.1607058304.git.luto@kernel.org

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Andy Lutomirski 2020-12-03 21:07:05 -08:00 • committed by Thomas Gleixner

parent 2ecedd7569

commit 758c9373d8

1 changed files with 18 additions and 0 deletions

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kernel/sched/membarrier.c

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