[PATCH] lockdep: Show up to three levels for a deadlock scenario
From: Steven Rostedt
Date: Thu Dec 14 2017 - 12:39:11 EST
Currently, when lockdep detects a possible deadlock scenario that involves 3
or more levels, it just shows the chain, and a CPU sequence order of the
first and last part of the scenario, leaving out the middle level and this
can take a bit of effort to understand. By adding a third level, it becomes
easier to see where the deadlock is.
The current output displays:
[For an AB BC CA scenario:]
Chain exists of:
lockC --> lockA --> lockB
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(lockB);
lock(lockA);
lock(lockB);
lock(lockC);
*** DEADLOCK ***
This change, now shows:
[For an AB BC CA scenario:]
Chain exists of:
lockC --> lockA --> lockB
Possible unsafe locking scenario:
CPU0 CPU1 CPU2
---- ---- ----
lock(lockB);
lock(lockA);
lock(lockC);
lock(lockA);
lock(lockB);
lock(lockC);
*** DEADLOCK ***
Much easier to see where the deadlock happened.
This also updates the interrupt scenario:
Old way:
Chain exists of:
lockA --> lockB --> lockC
Possible interrupt unsafe locking scenario:
CPU0 CPU1
---- ----
lock(lockC);
local_irq_disable();
lock(lockA);
lock(lockB);
<Interrupt>
lock(lockA);
*** DEADLOCK ***
New way:
Chain exists of:
lockA --> lockB --> lockC
Possible interrupt unsafe locking scenario:
CPU0 CPU1 CPU2
---- ---- ----
lock(lockC);
local_irq_disable();
lock(lockB);
local_irq_disable();
lock(lockA);
lock(lockB);
lock(lockC);
<Interrupt>
lock(lockA);
*** DEADLOCK ***
As well as for completions:
Old way:
Chain exists of:
mutexB --> mutexA --> (completion)&comp
Possible unsafe locking scenario by crosslock:
CPU0 CPU1
---- ----
lock(mutexA);
lock((completion)&comp);
lock(mutexB);
unlock((completion)&comp);
*** DEADLOCK ***
New way:
Chain exists of:
mutexB --> mutexA --> (completion)&comp
Possible unsafe locking scenario by crosslock:
CPU0 CPU1 CPU2
---- ---- ----
lock(mutexA);
lock((completion)&comp);
lock(mutexB);
lock(mutexA);
lock(mutexB);
unlock((completion)&comp);
*** DEADLOCK ***
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
kernel/locking/lockdep.c | 72 ++++++++++++++++++++++++++++++++++++++++--------
1 file changed, 61 insertions(+), 11 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index db933d063bfc..be15f86d47f0 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1128,6 +1128,7 @@ print_circular_lock_scenario(struct held_lock *src,
struct lock_class *source = hlock_class(src);
struct lock_class *target = hlock_class(tgt);
struct lock_class *parent = prt->class;
+ const char *spaces = "";
/*
* A direct locking problem where unsafe_class lock is taken
@@ -1154,31 +1155,61 @@ print_circular_lock_scenario(struct held_lock *src,
if (cross_lock(tgt->instance)) {
printk(" Possible unsafe locking scenario by crosslock:\n\n");
- printk(" CPU0 CPU1\n");
- printk(" ---- ----\n");
+ printk(" CPU0 CPU1");
+ if (parent != source)
+ printk(KERN_CONT " CPU2");
+ printk(KERN_CONT "\n");
+ printk(" ---- ----");
+ if (parent != source)
+ printk(KERN_CONT " ----");
+ printk(KERN_CONT "\n");
printk(" lock(");
__print_lock_name(parent);
printk(KERN_CONT ");\n");
printk(" lock(");
__print_lock_name(target);
printk(KERN_CONT ");\n");
- printk(" lock(");
+ if (parent != source) {
+ printk(" lock(");
+ __print_lock_name(source);
+ printk(KERN_CONT ");\n");
+ printk(" lock(");
+ __print_lock_name(parent);
+ printk(KERN_CONT ");\n");
+ spaces = " ";
+ }
+ printk("%s lock(", spaces);
__print_lock_name(source);
printk(KERN_CONT ");\n");
- printk(" unlock(");
+ printk("%s unlock(",spaces);
__print_lock_name(target);
printk(KERN_CONT ");\n");
printk("\n *** DEADLOCK ***\n\n");
} else {
printk(" Possible unsafe locking scenario:\n\n");
- printk(" CPU0 CPU1\n");
- printk(" ---- ----\n");
+ printk(" CPU0 CPU1");
+ if (parent != source)
+ printk(KERN_CONT " CPU2");
+ printk(KERN_CONT "\n");
+ printk(" ---- ----");
+ if (parent != source)
+ printk(KERN_CONT " ----");
+ printk(KERN_CONT "\n");
printk(" lock(");
__print_lock_name(target);
printk(KERN_CONT ");\n");
printk(" lock(");
__print_lock_name(parent);
printk(KERN_CONT ");\n");
+ if (parent != source) {
+ spaces = " ";
+ printk("%s lock(", spaces);
+ __print_lock_name(source);
+ printk(KERN_CONT ");\n");
+ printk("%s lock(", spaces);
+ __print_lock_name(parent);
+ printk(KERN_CONT ");\n");
+ }
printk(" lock(");
__print_lock_name(target);
printk(KERN_CONT ");\n");
@@ -1500,6 +1531,7 @@ print_irq_lock_scenario(struct lock_list *safe_entry,
struct lock_class *safe_class = safe_entry->class;
struct lock_class *unsafe_class = unsafe_entry->class;
struct lock_class *middle_class = prev_class;
+ const char *spaces = "";
if (middle_class == safe_class)
middle_class = next_class;
@@ -1528,18 +1560,36 @@ print_irq_lock_scenario(struct lock_list *safe_entry,
}
printk(" Possible interrupt unsafe locking scenario:\n\n");
- printk(" CPU0 CPU1\n");
- printk(" ---- ----\n");
+ printk(" CPU0 CPU1");
+ if (middle_class != unsafe_class)
+ printk(KERN_CONT " CPU2");
+ printk(KERN_CONT "\n");
+ printk(" ---- ----");
+ if (middle_class != unsafe_class)
+ printk(KERN_CONT " ----");
+ printk(KERN_CONT "\n");
printk(" lock(");
__print_lock_name(unsafe_class);
printk(KERN_CONT ");\n");
- printk(" local_irq_disable();\n");
- printk(" lock(");
+ if (middle_class != unsafe_class) {
+ spaces = " ";
+ printk(" local_irq_disable();\n");
+ printk(" lock(");
+ __print_lock_name(middle_class);
+ printk(KERN_CONT ");\n");
+ }
+ printk("%s local_irq_disable();\n", spaces);
+ printk("%s lock(", spaces);
__print_lock_name(safe_class);
printk(KERN_CONT ");\n");
- printk(" lock(");
+ printk("%s lock(", spaces);
__print_lock_name(middle_class);
printk(KERN_CONT ");\n");
+ if (middle_class != unsafe_class) {
+ printk(" lock(");
+ __print_lock_name(unsafe_class);
+ printk(KERN_CONT ");\n");
+ }
printk(" <Interrupt>\n");
printk(" lock(");
__print_lock_name(safe_class);
--
2.13.6