Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH tip/core/rcu 50/55] rcu: Inform the user about dynticks-idle mode on PROVE_RCU warning | Date | Tue, 6 Sep 2011 11:00:44 -0700 |
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From: Frederic Weisbecker <fweisbec@gmail.com>
Inform the user if an RCU usage error is detected by lockdep while in an extended quiescent state (in this case, dyntick-idle mode). This is accomplished by adding a line to the RCU lockdep splat indicating whether or not the splat occurred in dyntick-idle mode.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> --- kernel/lockdep.c | 20 ++++++++++++++++++++ 1 files changed, 20 insertions(+), 0 deletions(-)
diff --git a/kernel/lockdep.c b/kernel/lockdep.c index df2ad37..ef5dd69 100644 --- a/kernel/lockdep.c +++ b/kernel/lockdep.c @@ -4008,6 +4008,26 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s) 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); + + /* + * If a CPU is in dyntick-idle mode (CONFIG_NO_HZ), then RCU + * considers that CPU to be in an "extended quiescent state", + * which means that RCU will be completely ignoring that CPU. + * Therefore, rcu_read_lock() and friends have absolutely no + * effect on a dyntick-idle CPU. In other words, even if a + * dyntick-idle CPU has called rcu_read_lock(), RCU might well + * delete data structures out from under it. RCU really has no + * choice here: if it were to consult the CPU, that would wake + * the CPU up, and the whole point of dyntick-idle mode is to + * allow CPUs to enter extremely deep sleep states. + * + * So complain bitterly if someone does call rcu_read_lock(), + * rcu_read_lock_bh() and so on from extended quiescent states + * such as dyntick-idle mode. + */ + if (rcu_check_extended_qs()) + printk("RCU used illegally from extended quiescent state!\n"); + lockdep_print_held_locks(curr); printk("\nstack backtrace:\n"); dump_stack(); -- 1.7.3.2
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