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Fix: Disable sys_membarrier when nohz_full is enabled
commit 907565337e
upstream.
Userspace applications should be allowed to expect the membarrier system
call with MEMBARRIER_CMD_SHARED command to issue memory barriers on
nohz_full CPUs, but synchronize_sched() does not take those into
account.
Given that we do not want unrelated processes to be able to affect
real-time sensitive nohz_full CPUs, simply return ENOSYS when membarrier
is invoked on a kernel with enabled nohz_full CPUs.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Josh Triplett <josh@joshtriplett.org>
CC: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Rik van Riel <riel@redhat.com>
Acked-by: Lai Jiangshan <jiangshanlai@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -16,6 +16,7 @@
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#include <linux/syscalls.h>
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#include <linux/membarrier.h>
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#include <linux/tick.h>
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/*
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* Bitmask made from a "or" of all commands within enum membarrier_cmd,
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@ -51,6 +52,9 @@
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*/
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SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
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{
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/* MEMBARRIER_CMD_SHARED is not compatible with nohz_full. */
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if (tick_nohz_full_enabled())
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return -ENOSYS;
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if (unlikely(flags))
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return -EINVAL;
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switch (cmd) {
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