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authorpeterz@infradead.org <peterz@infradead.org>2020-09-02 18:03:23 +0200
committerIngo Molnar <mingo@kernel.org>2020-09-03 11:19:42 +0200
commit23870f1227680d2aacff6f79c3ab2222bd04e86e (patch)
tree46cfafbbcc57f372200072c6784d91145c6b6984
parentfc3abb53250a90ba2150eebd182137c136f4d25a (diff)
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locking/lockdep: Fix "USED" <- "IN-NMI" inversions
During the LPC RCU BoF Paul asked how come the "USED" <- "IN-NMI" detector doesn't trip over rcu_read_lock()'s lockdep annotation. Looking into this I found a very embarrasing typo in verify_lock_unused(): - if (!(class->usage_mask & LOCK_USED)) + if (!(class->usage_mask & LOCKF_USED)) fixing that will indeed cause rcu_read_lock() to insta-splat :/ The above typo means that instead of testing for: 0x100 (1 << LOCK_USED), we test for 8 (LOCK_USED), which corresponds to (1 << LOCK_ENABLED_HARDIRQ). So instead of testing for _any_ used lock, it will only match any lock used with interrupts enabled. The rcu_read_lock() annotation uses .check=0, which means it will not set any of the interrupt bits and will thus never match. In order to properly fix the situation and allow rcu_read_lock() to correctly work, split LOCK_USED into LOCK_USED and LOCK_USED_READ and by having .read users set USED_READ and test USED, pure read-recursive locks are permitted. Fixes: f6f48e180404 ("lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions") Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Tested-by: Masami Hiramatsu <mhiramat@kernel.org> Acked-by: Paul E. McKenney <paulmck@kernel.org> Link: https://lore.kernel.org/r/20200902160323.GK1362448@hirez.programming.kicks-ass.net
-rw-r--r--kernel/locking/lockdep.c35
-rw-r--r--kernel/locking/lockdep_internals.h2
2 files changed, 31 insertions, 6 deletions
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 54b74fabf40c..2facbbd146ec 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3969,13 +3969,18 @@ static int separate_irq_context(struct task_struct *curr,
static int mark_lock(struct task_struct *curr, struct held_lock *this,
enum lock_usage_bit new_bit)
{
- unsigned int new_mask = 1 << new_bit, ret = 1;
+ unsigned int old_mask, new_mask, ret = 1;
if (new_bit >= LOCK_USAGE_STATES) {
DEBUG_LOCKS_WARN_ON(1);
return 0;
}
+ if (new_bit == LOCK_USED && this->read)
+ new_bit = LOCK_USED_READ;
+
+ new_mask = 1 << new_bit;
+
/*
* If already set then do not dirty the cacheline,
* nor do any checks:
@@ -3988,13 +3993,22 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this,
/*
* Make sure we didn't race:
*/
- if (unlikely(hlock_class(this)->usage_mask & new_mask)) {
- graph_unlock();
- return 1;
- }
+ if (unlikely(hlock_class(this)->usage_mask & new_mask))
+ goto unlock;
+ old_mask = hlock_class(this)->usage_mask;
hlock_class(this)->usage_mask |= new_mask;
+ /*
+ * Save one usage_traces[] entry and map both LOCK_USED and
+ * LOCK_USED_READ onto the same entry.
+ */
+ if (new_bit == LOCK_USED || new_bit == LOCK_USED_READ) {
+ if (old_mask & (LOCKF_USED | LOCKF_USED_READ))
+ goto unlock;
+ new_bit = LOCK_USED;
+ }
+
if (!(hlock_class(this)->usage_traces[new_bit] = save_trace()))
return 0;
@@ -4008,6 +4022,7 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this,
return 0;
}
+unlock:
graph_unlock();
/*
@@ -4942,12 +4957,20 @@ static void verify_lock_unused(struct lockdep_map *lock, struct held_lock *hlock
{
#ifdef CONFIG_PROVE_LOCKING
struct lock_class *class = look_up_lock_class(lock, subclass);
+ unsigned long mask = LOCKF_USED;
/* if it doesn't have a class (yet), it certainly hasn't been used yet */
if (!class)
return;
- if (!(class->usage_mask & LOCK_USED))
+ /*
+ * READ locks only conflict with USED, such that if we only ever use
+ * READ locks, there is no deadlock possible -- RCU.
+ */
+ if (!hlock->read)
+ mask |= LOCKF_USED_READ;
+
+ if (!(class->usage_mask & mask))
return;
hlock->class_idx = class - lock_classes;
diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index baca699b94e9..b0be1560ed17 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -19,6 +19,7 @@ enum lock_usage_bit {
#include "lockdep_states.h"
#undef LOCKDEP_STATE
LOCK_USED,
+ LOCK_USED_READ,
LOCK_USAGE_STATES
};
@@ -40,6 +41,7 @@ enum {
#include "lockdep_states.h"
#undef LOCKDEP_STATE
__LOCKF(USED)
+ __LOCKF(USED_READ)
};
#define LOCKDEP_STATE(__STATE) LOCKF_ENABLED_##__STATE |