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Message-ID: <20150418151542.GA3551@gmail.com>
Date: Sat, 18 Apr 2015 17:15:42 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
"Paul E. McKenney" <paulmck@...ibm.com>,
Thomas Gleixner <tglx@...utronix.de>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: [GIT PULL] locking fixes
Linus,
Please pull the latest locking-urgent-for-linus git tree from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git locking-urgent-for-linus
# HEAD: 8053871d0f7f67c7efb7f226ef031f78877d6625 smp: Fix smp_call_function_single_async() locking
Two fixes: your smp-call fix and a lockdep fix.
Thanks,
Ingo
------------------>
Linus Torvalds (1):
smp: Fix smp_call_function_single_async() locking
Peter Zijlstra (1):
lockdep: Make print_lock() robust against concurrent release
kernel/locking/lockdep.c | 16 +++++++++-
kernel/smp.c | 78 +++++++++++++++++++++++++++++-------------------
2 files changed, 62 insertions(+), 32 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index ba77ab5f64dd..a0831e1b99f4 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -551,7 +551,21 @@ static void print_lockdep_cache(struct lockdep_map *lock)
static void print_lock(struct held_lock *hlock)
{
- print_lock_name(hlock_class(hlock));
+ /*
+ * We can be called locklessly through debug_show_all_locks() so be
+ * extra careful, the hlock might have been released and cleared.
+ */
+ unsigned int class_idx = hlock->class_idx;
+
+ /* Don't re-read hlock->class_idx, can't use READ_ONCE() on bitfields: */
+ barrier();
+
+ if (!class_idx || (class_idx - 1) >= MAX_LOCKDEP_KEYS) {
+ printk("<RELEASED>\n");
+ return;
+ }
+
+ print_lock_name(lock_classes + class_idx - 1);
printk(", at: ");
print_ip_sym(hlock->acquire_ip);
}
diff --git a/kernel/smp.c b/kernel/smp.c
index f38a1e692259..2aaac2c47683 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -19,7 +19,7 @@
enum {
CSD_FLAG_LOCK = 0x01,
- CSD_FLAG_WAIT = 0x02,
+ CSD_FLAG_SYNCHRONOUS = 0x02,
};
struct call_function_data {
@@ -107,7 +107,7 @@ void __init call_function_init(void)
*/
static void csd_lock_wait(struct call_single_data *csd)
{
- while (csd->flags & CSD_FLAG_LOCK)
+ while (smp_load_acquire(&csd->flags) & CSD_FLAG_LOCK)
cpu_relax();
}
@@ -121,19 +121,17 @@ static void csd_lock(struct call_single_data *csd)
* to ->flags with any subsequent assignments to other
* fields of the specified call_single_data structure:
*/
- smp_mb();
+ smp_wmb();
}
static void csd_unlock(struct call_single_data *csd)
{
- WARN_ON((csd->flags & CSD_FLAG_WAIT) && !(csd->flags & CSD_FLAG_LOCK));
+ WARN_ON(!(csd->flags & CSD_FLAG_LOCK));
/*
* ensure we're all done before releasing data:
*/
- smp_mb();
-
- csd->flags &= ~CSD_FLAG_LOCK;
+ smp_store_release(&csd->flags, 0);
}
static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_single_data, csd_data);
@@ -144,13 +142,16 @@ static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_single_data, csd_data);
* ->func, ->info, and ->flags set.
*/
static int generic_exec_single(int cpu, struct call_single_data *csd,
- smp_call_func_t func, void *info, int wait)
+ smp_call_func_t func, void *info)
{
- struct call_single_data csd_stack = { .flags = 0 };
- unsigned long flags;
-
-
if (cpu == smp_processor_id()) {
+ unsigned long flags;
+
+ /*
+ * We can unlock early even for the synchronous on-stack case,
+ * since we're doing this from the same CPU..
+ */
+ csd_unlock(csd);
local_irq_save(flags);
func(info);
local_irq_restore(flags);
@@ -161,21 +162,9 @@ static int generic_exec_single(int cpu, struct call_single_data *csd,
if ((unsigned)cpu >= nr_cpu_ids || !cpu_online(cpu))
return -ENXIO;
-
- if (!csd) {
- csd = &csd_stack;
- if (!wait)
- csd = this_cpu_ptr(&csd_data);
- }
-
- csd_lock(csd);
-
csd->func = func;
csd->info = info;
- if (wait)
- csd->flags |= CSD_FLAG_WAIT;
-
/*
* The list addition should be visible before sending the IPI
* handler locks the list to pull the entry off it because of
@@ -190,9 +179,6 @@ static int generic_exec_single(int cpu, struct call_single_data *csd,
if (llist_add(&csd->llist, &per_cpu(call_single_queue, cpu)))
arch_send_call_function_single_ipi(cpu);
- if (wait)
- csd_lock_wait(csd);
-
return 0;
}
@@ -250,8 +236,17 @@ static void flush_smp_call_function_queue(bool warn_cpu_offline)
}
llist_for_each_entry_safe(csd, csd_next, entry, llist) {
- csd->func(csd->info);
- csd_unlock(csd);
+ smp_call_func_t func = csd->func;
+ void *info = csd->info;
+
+ /* Do we wait until *after* callback? */
+ if (csd->flags & CSD_FLAG_SYNCHRONOUS) {
+ func(info);
+ csd_unlock(csd);
+ } else {
+ csd_unlock(csd);
+ func(info);
+ }
}
/*
@@ -274,6 +269,8 @@ static void flush_smp_call_function_queue(bool warn_cpu_offline)
int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
int wait)
{
+ struct call_single_data *csd;
+ struct call_single_data csd_stack = { .flags = CSD_FLAG_LOCK | CSD_FLAG_SYNCHRONOUS };
int this_cpu;
int err;
@@ -292,7 +289,16 @@ 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);
- err = generic_exec_single(cpu, NULL, func, info, wait);
+ csd = &csd_stack;
+ if (!wait) {
+ csd = this_cpu_ptr(&csd_data);
+ csd_lock(csd);
+ }
+
+ err = generic_exec_single(cpu, csd, func, info);
+
+ if (wait)
+ csd_lock_wait(csd);
put_cpu();
@@ -321,7 +327,15 @@ int smp_call_function_single_async(int cpu, struct call_single_data *csd)
int err = 0;
preempt_disable();
- err = generic_exec_single(cpu, csd, csd->func, csd->info, 0);
+
+ /* We could deadlock if we have to wait here with interrupts disabled! */
+ if (WARN_ON_ONCE(csd->flags & CSD_FLAG_LOCK))
+ csd_lock_wait(csd);
+
+ csd->flags = CSD_FLAG_LOCK;
+ smp_wmb();
+
+ err = generic_exec_single(cpu, csd, csd->func, csd->info);
preempt_enable();
return err;
@@ -433,6 +447,8 @@ void smp_call_function_many(const struct cpumask *mask,
struct call_single_data *csd = per_cpu_ptr(cfd->csd, cpu);
csd_lock(csd);
+ if (wait)
+ csd->flags |= CSD_FLAG_SYNCHRONOUS;
csd->func = func;
csd->info = info;
llist_add(&csd->llist, &per_cpu(call_single_queue, cpu));
--
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