linux-kernel - [tip:smp/urgent] smp: Warn on function calls from softirq context

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Date:   Sat, 20 Jul 2019 02:31:57 -0700
From:   tip-bot for Peter Zijlstra <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     peterz@...radead.org, linux-kernel@...r.kernel.org,
        luferry@....com, hpa@...or.com, mingo@...nel.org,
        tglx@...utronix.de
Subject: [tip:smp/urgent] smp: Warn on function calls from softirq context

Commit-ID:  19dbdcb8039cff16669a05136a29180778d16d0a
Gitweb:     https://git.kernel.org/tip/19dbdcb8039cff16669a05136a29180778d16d0a
Author:     Peter Zijlstra <peterz@...radead.org>
AuthorDate: Thu, 18 Jul 2019 11:20:09 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Sat, 20 Jul 2019 11:27:16 +0200

smp: Warn on function calls from softirq context

It's clearly documented that smp function calls cannot be invoked from
softirq handling context. Unfortunately nothing enforces that or emits a
warning.

A single function call can be invoked from softirq context only via
smp_call_function_single_async().

The only legit context is task context, so add a warning to that effect.

Reported-by: luferry <luferry@....com>
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lkml.kernel.org/r/20190718160601.GP3402@hirez.programming.kicks-ass.net
---
 kernel/smp.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/kernel/smp.c b/kernel/smp.c
index 616d4d114847..7dbcb402c2fc 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -291,6 +291,14 @@ int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
 	WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
 		     && !oops_in_progress);
 
+	/*
+	 * When @wait we can deadlock when we interrupt between llist_add() and
+	 * arch_send_call_function_ipi*(); when !@...t we can deadlock due to
+	 * csd_lock() on because the interrupt context uses the same csd
+	 * storage.
+	 */
+	WARN_ON_ONCE(!in_task());
+
 	csd = &csd_stack;
 	if (!wait) {
 		csd = this_cpu_ptr(&csd_data);
@@ -416,6 +424,14 @@ void smp_call_function_many(const struct cpumask *mask,
 	WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
 		     && !oops_in_progress && !early_boot_irqs_disabled);
 
+	/*
+	 * When @wait we can deadlock when we interrupt between llist_add() and
+	 * arch_send_call_function_ipi*(); when !@...t we can deadlock due to
+	 * csd_lock() on because the interrupt context uses the same csd
+	 * storage.
+	 */
+	WARN_ON_ONCE(!in_task());
+
 	/* Try to fastpath.  So, what's a CPU they want? Ignoring this one. */
 	cpu = cpumask_first_and(mask, cpu_online_mask);
 	if (cpu == this_cpu)