Skip to content

Commit

Permalink
rcu: Restore checks for blocking in RCU read-side critical sections
Browse files Browse the repository at this point in the history 
Long ago, using TREE_RCU with PREEMPT would result in "scheduling
while atomic" diagnostics if you blocked in an RCU read-side critical
section.  However, PREEMPT now implies TREE_PREEMPT_RCU, which defeats
this diagnostic.  This commit therefore adds a replacement diagnostic
based on PROVE_RCU.

Because rcu_lockdep_assert() and lockdep_rcu_dereference() are now being
used for things that have nothing to do with rcu_dereference(), rename
lockdep_rcu_dereference() to lockdep_rcu_suspicious() and add a third
argument that is a string indicating what is suspicious.  This third
argument is passed in from a new third argument to rcu_lockdep_assert().
Update all calls to rcu_lockdep_assert() to add an informative third
argument.

Also, add a pair of rcu_lockdep_assert() calls from within
rcu_note_context_switch(), one complaining if a context switch occurs
in an RCU-bh read-side critical section and another complaining if a
context switch occurs in an RCU-sched read-side critical section.
These are present only if the PROVE_RCU kernel parameter is enabled.

Finally, fix some checkpatch whitespace complaints in lockdep.c.

Again, you must enable PROVE_RCU to see these new diagnostics.  But you
are enabling PROVE_RCU to check out new RCU uses in any case, aren't you?

Signed-off-by: Paul E. McKenney <[email protected]>
  • Loading branch information
@paulmck
paulmck committed Sep 29, 2011
1 parent d5988af commit b3fbab0
Show file tree
Hide file tree
Showing 5 changed files with 75 additions and 45 deletions.
2 changes: 1 addition & 1 deletion include/linux/lockdep.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -548,7 +548,7 @@ do { \
#endif

#ifdef CONFIG_PROVE_RCU
extern void lockdep_rcu_dereference(const char *file, const int line);
void lockdep_rcu_suspicious(const char *file, const int line, const char *s);
#endif

#endif /* __LINUX_LOCKDEP_H */
28 changes: 22 additions & 6 deletions include/linux/rcupdate.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -297,19 +297,31 @@ extern int rcu_my_thread_group_empty(void);
/**
* rcu_lockdep_assert - emit lockdep splat if specified condition not met
* @c: condition to check
* @s: informative message
*/
#define rcu_lockdep_assert(c) \
#define rcu_lockdep_assert(c, s) \
do { \
static bool __warned; \
if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
__warned = true; \
lockdep_rcu_dereference(__FILE__, __LINE__); \
lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
} \
} while (0)

#define rcu_sleep_check() \
do { \
rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \
"Illegal context switch in RCU-bh" \
" read-side critical section"); \
rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), \
"Illegal context switch in RCU-sched"\
" read-side critical section"); \
} while (0)

#else /* #ifdef CONFIG_PROVE_RCU */

#define rcu_lockdep_assert(c) do { } while (0)
#define rcu_lockdep_assert(c, s) do { } while (0)
#define rcu_sleep_check() do { } while (0)

#endif /* #else #ifdef CONFIG_PROVE_RCU */

Expand Down Expand Up @@ -338,14 +350,16 @@ extern int rcu_my_thread_group_empty(void);
#define __rcu_dereference_check(p, c, space) \
({ \
typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
rcu_lockdep_assert(c); \
rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \
" usage"); \
rcu_dereference_sparse(p, space); \
smp_read_barrier_depends(); \
((typeof(*p) __force __kernel *)(_________p1)); \
})
#define __rcu_dereference_protected(p, c, space) \
({ \
rcu_lockdep_assert(c); \
rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \
" usage"); \
rcu_dereference_sparse(p, space); \
((typeof(*p) __force __kernel *)(p)); \
})
Expand All @@ -359,7 +373,9 @@ extern int rcu_my_thread_group_empty(void);
#define __rcu_dereference_index_check(p, c) \
({ \
typeof(p) _________p1 = ACCESS_ONCE(p); \
rcu_lockdep_assert(c); \
rcu_lockdep_assert(c, \
"suspicious rcu_dereference_index_check()" \
" usage"); \
smp_read_barrier_depends(); \
(_________p1); \
})
Expand Down
84 changes: 47 additions & 37 deletions kernel/lockdep.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1129,10 +1129,11 @@ print_circular_bug_header(struct lock_list *entry, unsigned int depth,
if (debug_locks_silent)
return 0;

printk("\n=======================================================\n");
printk( "[ INFO: possible circular locking dependency detected ]\n");
printk("\n");
printk("======================================================\n");
printk("[ INFO: possible circular locking dependency detected ]\n");
print_kernel_version();
printk( "-------------------------------------------------------\n");
printk("-------------------------------------------------------\n");
printk("%s/%d is trying to acquire lock:\n",
curr->comm, task_pid_nr(curr));
print_lock(check_src);
Expand Down Expand Up @@ -1463,11 +1464,12 @@ print_bad_irq_dependency(struct task_struct *curr,
if (!debug_locks_off_graph_unlock() || debug_locks_silent)
return 0;

printk("\n======================================================\n");
printk( "[ INFO: %s-safe -> %s-unsafe lock order detected ]\n",
printk("\n");
printk("======================================================\n");
printk("[ INFO: %s-safe -> %s-unsafe lock order detected ]\n",
irqclass, irqclass);
print_kernel_version();
printk( "------------------------------------------------------\n");
printk("------------------------------------------------------\n");
printk("%s/%d [HC%u[%lu]:SC%u[%lu]:HE%u:SE%u] is trying to acquire:\n",
curr->comm, task_pid_nr(curr),
curr->hardirq_context, hardirq_count() >> HARDIRQ_SHIFT,
Expand Down Expand Up @@ -1692,10 +1694,11 @@ print_deadlock_bug(struct task_struct *curr, struct held_lock *prev,
if (!debug_locks_off_graph_unlock() || debug_locks_silent)
return 0;

printk("\n=============================================\n");
printk( "[ INFO: possible recursive locking detected ]\n");
printk("\n");
printk("=============================================\n");
printk("[ INFO: possible recursive locking detected ]\n");
print_kernel_version();
printk( "---------------------------------------------\n");
printk("---------------------------------------------\n");
printk("%s/%d is trying to acquire lock:\n",
curr->comm, task_pid_nr(curr));
print_lock(next);
Expand Down Expand Up @@ -2177,10 +2180,11 @@ print_usage_bug(struct task_struct *curr, struct held_lock *this,
if (!debug_locks_off_graph_unlock() || debug_locks_silent)
return 0;

printk("\n=================================\n");
printk( "[ INFO: inconsistent lock state ]\n");
printk("\n");
printk("=================================\n");
printk("[ INFO: inconsistent lock state ]\n");
print_kernel_version();
printk( "---------------------------------\n");
printk("---------------------------------\n");

printk("inconsistent {%s} -> {%s} usage.\n",
usage_str[prev_bit], usage_str[new_bit]);
Expand Down Expand Up @@ -2241,10 +2245,11 @@ print_irq_inversion_bug(struct task_struct *curr,
if (!debug_locks_off_graph_unlock() || debug_locks_silent)
return 0;

printk("\n=========================================================\n");
printk( "[ INFO: possible irq lock inversion dependency detected ]\n");
printk("\n");
printk("=========================================================\n");
printk("[ INFO: possible irq lock inversion dependency detected ]\n");
print_kernel_version();
printk( "---------------------------------------------------------\n");
printk("---------------------------------------------------------\n");
printk("%s/%d just changed the state of lock:\n",
curr->comm, task_pid_nr(curr));
print_lock(this);
Expand Down Expand Up @@ -3065,9 +3070,10 @@ print_unlock_inbalance_bug(struct task_struct *curr, struct lockdep_map *lock,
if (debug_locks_silent)
return 0;

printk("\n=====================================\n");
printk( "[ BUG: bad unlock balance detected! ]\n");
printk( "-------------------------------------\n");
printk("\n");
printk("=====================================\n");
printk("[ BUG: bad unlock balance detected! ]\n");
printk("-------------------------------------\n");
printk("%s/%d is trying to release lock (",
curr->comm, task_pid_nr(curr));
print_lockdep_cache(lock);
Expand Down Expand Up @@ -3478,9 +3484,10 @@ print_lock_contention_bug(struct task_struct *curr, struct lockdep_map *lock,
if (debug_locks_silent)
return 0;

printk("\n=================================\n");
printk( "[ BUG: bad contention detected! ]\n");
printk( "---------------------------------\n");
printk("\n");
printk("=================================\n");
printk("[ BUG: bad contention detected! ]\n");
printk("---------------------------------\n");
printk("%s/%d is trying to contend lock (",
curr->comm, task_pid_nr(curr));
print_lockdep_cache(lock);
Expand Down Expand Up @@ -3839,9 +3846,10 @@ print_freed_lock_bug(struct task_struct *curr, const void *mem_from,
if (debug_locks_silent)
return;

printk("\n=========================\n");
printk( "[ BUG: held lock freed! ]\n");
printk( "-------------------------\n");
printk("\n");
printk("=========================\n");
printk("[ BUG: held lock freed! ]\n");
printk("-------------------------\n");
printk("%s/%d is freeing memory %p-%p, with a lock still held there!\n",
curr->comm, task_pid_nr(curr), mem_from, mem_to-1);
print_lock(hlock);
Expand Down Expand Up @@ -3895,9 +3903,10 @@ static void print_held_locks_bug(struct task_struct *curr)
if (debug_locks_silent)
return;

printk("\n=====================================\n");
printk( "[ BUG: lock held at task exit time! ]\n");
printk( "-------------------------------------\n");
printk("\n");
printk("=====================================\n");
printk("[ BUG: lock held at task exit time! ]\n");
printk("-------------------------------------\n");
printk("%s/%d is exiting with locks still held!\n",
curr->comm, task_pid_nr(curr));
lockdep_print_held_locks(curr);
Expand Down Expand Up @@ -3991,16 +4000,17 @@ void lockdep_sys_exit(void)
if (unlikely(curr->lockdep_depth)) {
if (!debug_locks_off())
return;
printk("\n================================================\n");
printk( "[ BUG: lock held when returning to user space! ]\n");
printk( "------------------------------------------------\n");
printk("\n");
printk("================================================\n");
printk("[ BUG: lock held when returning to user space! ]\n");
printk("------------------------------------------------\n");
printk("%s/%d is leaving the kernel with locks still held!\n",
curr->comm, curr->pid);
lockdep_print_held_locks(curr);
}
}

void lockdep_rcu_dereference(const char *file, const int line)
void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
{
struct task_struct *curr = current;

Expand All @@ -4009,15 +4019,15 @@ void lockdep_rcu_dereference(const char *file, const int line)
return;
#endif /* #ifdef CONFIG_PROVE_RCU_REPEATEDLY */
/* Note: the following can be executed concurrently, so be careful. */
printk("\n===================================================\n");
printk( "[ INFO: suspicious rcu_dereference_check() usage. ]\n");
printk( "---------------------------------------------------\n");
printk("%s:%d invoked rcu_dereference_check() without protection!\n",
file, line);
printk("\n");
printk("===============================\n");
printk("[ INFO: suspicious RCU usage. ]\n");
printk("-------------------------------\n");
printk("%s:%d %s!\n", file, line, s);
printk("\nother info that might help us debug this:\n\n");
printk("\nrcu_scheduler_active = %d, debug_locks = %d\n", rcu_scheduler_active, debug_locks);
lockdep_print_held_locks(curr);
printk("\nstack backtrace:\n");
dump_stack();
}
EXPORT_SYMBOL_GPL(lockdep_rcu_dereference);
EXPORT_SYMBOL_GPL(lockdep_rcu_suspicious);
4 changes: 3 additions & 1 deletion kernel/pid.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -418,7 +418,9 @@ EXPORT_SYMBOL(pid_task);
*/
struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
{
rcu_lockdep_assert(rcu_read_lock_held());
rcu_lockdep_assert(rcu_read_lock_held(),
"find_task_by_pid_ns() needs rcu_read_lock()"
" protection");
return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
}

Expand Down
2 changes: 2 additions & 0 deletions kernel/sched.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -4237,6 +4237,7 @@ static inline void schedule_debug(struct task_struct *prev)
*/
if (unlikely(in_atomic_preempt_off() && !prev->exit_state))
__schedule_bug(prev);
rcu_sleep_check();

profile_hit(SCHED_PROFILING, __builtin_return_address(0));

Expand Down Expand Up @@ -8230,6 +8231,7 @@ void __might_sleep(const char *file, int line, int preempt_offset)
{
static unsigned long prev_jiffy; /* ratelimiting */

rcu_sleep_check(); /* WARN_ON_ONCE() by default, no rate limit reqd. */
if ((preempt_count_equals(preempt_offset) && !irqs_disabled()) ||
system_state != SYSTEM_RUNNING || oops_in_progress)
return;
Expand Down

0 comments on commit b3fbab0

Please sign in to comment.