Remove the IPI fallback code from membarrier to deal with very infrequent cpumask memory allocation failure. Use GFP_KERNEL rather than GFP_NOWAIT, and relax the blocking guarantees for the expedited membarrier system call commands, allowing it to block if waiting for memory to be made available.
In addition, now -ENOMEM can be returned to user-space if the cpumask memory allocation fails. Signed-off-by: Mathieu Desnoyers <[email protected]> Cc: "Paul E. McKenney" <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Oleg Nesterov <[email protected]> Cc: "Eric W. Biederman" <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Russell King - ARM Linux admin <[email protected]> Cc: Chris Metcalf <[email protected]> Cc: Christoph Lameter <[email protected]> Cc: Kirill Tkhai <[email protected]> Cc: Mike Galbraith <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Ingo Molnar <[email protected]> --- kernel/sched/membarrier.c | 61 ++++++++++++--------------------------- 1 file changed, 19 insertions(+), 42 deletions(-) diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c index 8afbdf92be0a..1420c656e8f0 100644 --- a/kernel/sched/membarrier.c +++ b/kernel/sched/membarrier.c @@ -66,7 +66,6 @@ void membarrier_exec_mmap(struct mm_struct *mm) static int membarrier_global_expedited(void) { int cpu; - bool fallback = false; cpumask_var_t tmpmask; if (num_online_cpus() == 1) @@ -78,15 +77,8 @@ static int membarrier_global_expedited(void) */ smp_mb(); /* system call entry is not a mb. */ - /* - * Expedited membarrier commands guarantee that they won't - * block, hence the GFP_NOWAIT allocation flag and fallback - * implementation. - */ - if (!zalloc_cpumask_var(&tmpmask, GFP_NOWAIT)) { - /* Fallback for OOM. */ - fallback = true; - } + if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL)) + return -ENOMEM; cpus_read_lock(); rcu_read_lock(); @@ -117,18 +109,15 @@ static int membarrier_global_expedited(void) if (p->flags & PF_KTHREAD) continue; - if (!fallback) - __cpumask_set_cpu(cpu, tmpmask); - else - smp_call_function_single(cpu, ipi_mb, NULL, 1); + __cpumask_set_cpu(cpu, tmpmask); } rcu_read_unlock(); - if (!fallback) { - preempt_disable(); - smp_call_function_many(tmpmask, ipi_mb, NULL, 1); - preempt_enable(); - free_cpumask_var(tmpmask); - } + + preempt_disable(); + smp_call_function_many(tmpmask, ipi_mb, NULL, 1); + preempt_enable(); + + free_cpumask_var(tmpmask); cpus_read_unlock(); /* @@ -143,7 +132,6 @@ static int membarrier_global_expedited(void) static int membarrier_private_expedited(int flags) { int cpu; - bool fallback = false; cpumask_var_t tmpmask; struct mm_struct *mm = current->mm; @@ -168,15 +156,8 @@ static int membarrier_private_expedited(int flags) */ smp_mb(); /* system call entry is not a mb. */ - /* - * Expedited membarrier commands guarantee that they won't - * block, hence the GFP_NOWAIT allocation flag and fallback - * implementation. - */ - if (!zalloc_cpumask_var(&tmpmask, GFP_NOWAIT)) { - /* Fallback for OOM. */ - fallback = true; - } + if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL)) + return -ENOMEM; cpus_read_lock(); rcu_read_lock(); @@ -194,20 +175,16 @@ static int membarrier_private_expedited(int flags) if (cpu == raw_smp_processor_id()) continue; p = task_rcu_dereference(&cpu_rq(cpu)->curr); - if (p && p->mm == mm) { - if (!fallback) - __cpumask_set_cpu(cpu, tmpmask); - else - smp_call_function_single(cpu, ipi_mb, NULL, 1); - } + if (p && p->mm == mm) + __cpumask_set_cpu(cpu, tmpmask); } rcu_read_unlock(); - if (!fallback) { - preempt_disable(); - smp_call_function_many(tmpmask, ipi_mb, NULL, 1); - preempt_enable(); - free_cpumask_var(tmpmask); - } + + preempt_disable(); + smp_call_function_many(tmpmask, ipi_mb, NULL, 1); + preempt_enable(); + + free_cpumask_var(tmpmask); cpus_read_unlock(); /* -- 2.17.1
