[PATCH tip/core/rcu 03/20] Fix: Disable sys_membarrier when nohz_full is enabled
From: Mathieu DesnoyersUserspace 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 CC: Josh Triplett CC: Steven Rostedt CC: [3.10+] Signed-off-by: Paul E. McKenney Cc: Frederic Weisbecker Cc: Chris Metcalf Cc: Rik van Riel Acked-by: Lai Jiangshan --- kernel/membarrier.c | 4 1 file changed, 4 insertions(+) diff --git a/kernel/membarrier.c b/kernel/membarrier.c index 536c727a56e9..9f9284f37f8d 100644 --- a/kernel/membarrier.c +++ b/kernel/membarrier.c @@ -16,6 +16,7 @@ #include #include +#include /* * Bitmask made from a "or" of all commands within enum membarrier_cmd, @@ -51,6 +52,9 @@ */ SYSCALL_DEFINE2(membarrier, int, cmd, int, flags) { + /* MEMBARRIER_CMD_SHARED is not compatible with nohz_full. */ + if (tick_nohz_full_enabled()) + return -ENOSYS; if (unlikely(flags)) return -EINVAL; switch (cmd) { -- 2.5.2
[PATCH tip/core/rcu 03/20] Fix: Disable sys_membarrier when nohz_full is enabled
From: Mathieu Desnoyers 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 CC: Josh Triplett CC: Steven Rostedt CC: [3.10+] Signed-off-by: Paul E. McKenney Cc: Frederic Weisbecker Cc: Chris Metcalf Cc: Rik van Riel Acked-by: Lai Jiangshan --- kernel/membarrier.c | 4 1 file changed, 4 insertions(+) diff --git a/kernel/membarrier.c b/kernel/membarrier.c index 536c727a56e9..9f9284f37f8d 100644 --- a/kernel/membarrier.c +++ b/kernel/membarrier.c @@ -16,6 +16,7 @@ #include #include +#include /* * Bitmask made from a "or" of all commands within enum membarrier_cmd, @@ -51,6 +52,9 @@ */ SYSCALL_DEFINE2(membarrier, int, cmd, int, flags) { + /* MEMBARRIER_CMD_SHARED is not compatible with nohz_full. */ + if (tick_nohz_full_enabled()) + return -ENOSYS; if (unlikely(flags)) return -EINVAL; switch (cmd) { -- 2.5.2