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Commit b3fbab05 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Restore checks for blocking in RCU read-side critical sections 



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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent d5988af5

include/linux/lockdep.h

+1 −1
Original line number Diff line number Diff line
@@ -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 */

include/linux/rcupdate.h

+22 −6
Original line number Diff line number Diff line
@@ -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 */
@@ -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)); \

	})
@@ -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); \

	})

kernel/lockdep.c

+47 −37
Original line number Diff line number Diff line
@@ -1129,7 +1129,8 @@ print_circular_bug_header(struct lock_list *entry, unsigned int depth, 
	if (debug_locks_silent)

		return 0;



	printk("\n=======================================================\n");

	printk("\n");

	printk("======================================================\n");

	printk("[ INFO: possible circular locking dependency detected ]\n");

	print_kernel_version();

	printk("-------------------------------------------------------\n");
@@ -1463,7 +1464,8 @@ print_bad_irq_dependency(struct task_struct *curr, 
	if (!debug_locks_off_graph_unlock() || debug_locks_silent)

		return 0;



	printk("\n======================================================\n");

	printk("\n");

	printk("======================================================\n");

	printk("[ INFO: %s-safe -> %s-unsafe lock order detected ]\n",

		irqclass, irqclass);

	print_kernel_version();
@@ -1692,7 +1694,8 @@ 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("\n");

	printk("=============================================\n");

	printk("[ INFO: possible recursive locking detected ]\n");

	print_kernel_version();

	printk("---------------------------------------------\n");
@@ -2177,7 +2180,8 @@ 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("\n");

	printk("=================================\n");

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

	print_kernel_version();

	printk("---------------------------------\n");
@@ -2241,7 +2245,8 @@ print_irq_inversion_bug(struct task_struct *curr, 
	if (!debug_locks_off_graph_unlock() || debug_locks_silent)

		return 0;



	printk("\n=========================================================\n");

	printk("\n");

	printk("=========================================================\n");

	printk("[ INFO: possible irq lock inversion dependency detected ]\n");

	print_kernel_version();

	printk("---------------------------------------------------------\n");
@@ -3065,7 +3070,8 @@ print_unlock_inbalance_bug(struct task_struct *curr, struct lockdep_map *lock, 
	if (debug_locks_silent)

		return 0;



	printk("\n=====================================\n");

	printk("\n");

	printk("=====================================\n");

	printk("[ BUG: bad unlock balance detected! ]\n");

	printk("-------------------------------------\n");

	printk("%s/%d is trying to release lock (",
@@ -3478,7 +3484,8 @@ print_lock_contention_bug(struct task_struct *curr, struct lockdep_map *lock, 
	if (debug_locks_silent)

		return 0;



	printk("\n=================================\n");

	printk("\n");

	printk("=================================\n");

	printk("[ BUG: bad contention detected! ]\n");

	printk("---------------------------------\n");

	printk("%s/%d is trying to contend lock (",
@@ -3839,7 +3846,8 @@ print_freed_lock_bug(struct task_struct *curr, const void *mem_from, 
	if (debug_locks_silent)

		return;



	printk("\n=========================\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",
@@ -3895,7 +3903,8 @@ static void print_held_locks_bug(struct task_struct *curr) 
	if (debug_locks_silent)

		return;



	printk("\n=====================================\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",
@@ -3991,7 +4000,8 @@ void lockdep_sys_exit(void) 
	if (unlikely(curr->lockdep_depth)) {

		if (!debug_locks_off())

			return;

		printk("\n================================================\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",
@@ -4000,7 +4010,7 @@ void lockdep_sys_exit(void) 
	}

}



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;
@@ -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);

kernel/pid.c

+3 −1
Original line number Diff line number Diff line
@@ -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);

}

kernel/sched.c

+2 −0
Original line number Diff line number Diff line
@@ -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));
@@ -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;