Messages in this thread Patch in this message | | | From | Mathieu Desnoyers <> | Subject | [RFC PATCH for 5.4 7/7] sched/membarrier: Return -ENOMEM to userspace on memory allocation failure | Date | Thu, 19 Sep 2019 13:37:05 -0400 |
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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 <mathieu.desnoyers@efficios.com> Cc: "Paul E. McKenney" <paulmck@linux.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Russell King - ARM Linux admin <linux@armlinux.org.uk> Cc: Chris Metcalf <cmetcalf@ezchip.com> Cc: Christoph Lameter <cl@linux.com> Cc: Kirill Tkhai <tkhai@yandex.ru> Cc: Mike Galbraith <efault@gmx.de> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@kernel.org> --- 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
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