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| author | Reinette Chatre <reinette.chatre@intel.com> | 2020-12-17 14:31:20 -0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2023-01-18 11:45:00 +0100 |
| commit | 446c7251f007282b5f9dd9853be8d6737cb3c14d (patch) | |
| tree | 091978d1fa88baef503070965ddef9e0497eb056 | |
| parent | 196c6f0c3e217223c060f5376f1095948df33781 (diff) | |
| download | linux-446c7251f007282b5f9dd9853be8d6737cb3c14d.tar.gz linux-446c7251f007282b5f9dd9853be8d6737cb3c14d.tar.bz2 linux-446c7251f007282b5f9dd9853be8d6737cb3c14d.zip | |
x86/resctrl: Use task_curr() instead of task_struct->on_cpu to prevent unnecessary IPI
[ Upstream commit e0ad6dc8969f790f14bddcfd7ea284b7e5f88a16 ]
James reported in [1] that there could be two tasks running on the same CPU
with task_struct->on_cpu set. Using task_struct->on_cpu as a test if a task
is running on a CPU may thus match the old task for a CPU while the
scheduler is running and IPI it unnecessarily.
task_curr() is the correct helper to use. While doing so move the #ifdef
check of the CONFIG_SMP symbol to be a C conditional used to determine
if this helper should be used to ensure the code is always checked for
correctness by the compiler.
[1] https://lore.kernel.org/lkml/a782d2f3-d2f6-795f-f4b1-9462205fd581@arm.com
Reported-by: James Morse <james.morse@arm.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/e9e68ce1441a73401e08b641cc3b9a3cf13fe6d4.1608243147.git.reinette.chatre@intel.com
Stable-dep-of: fe1f0714385f ("x86/resctrl: Fix task CLOSID/RMID update race")
Signed-off-by: Sasha Levin <sashal@kernel.org>
| -rw-r--r-- | arch/x86/kernel/cpu/resctrl/rdtgroup.c | 14 |
1 files changed, 5 insertions, 9 deletions
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c index 5a59e3315b34..f2ad3c117426 100644 --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c @@ -2313,19 +2313,15 @@ static void rdt_move_group_tasks(struct rdtgroup *from, struct rdtgroup *to, t->closid = to->closid; t->rmid = to->mon.rmid; -#ifdef CONFIG_SMP /* - * This is safe on x86 w/o barriers as the ordering - * of writing to task_cpu() and t->on_cpu is - * reverse to the reading here. The detection is - * inaccurate as tasks might move or schedule - * before the smp function call takes place. In - * such a case the function call is pointless, but + * If the task is on a CPU, set the CPU in the mask. + * The detection is inaccurate as tasks might move or + * schedule before the smp function call takes place. + * In such a case the function call is pointless, but * there is no other side effect. */ - if (mask && t->on_cpu) + if (IS_ENABLED(CONFIG_SMP) && mask && task_curr(t)) cpumask_set_cpu(task_cpu(t), mask); -#endif } } read_unlock(&tasklist_lock); |