Messages in this thread | | | Date | Thu, 2 Feb 2012 12:42:06 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH RFC tip/core/rcu 03/41] rcu: Add lockdep-RCU checks for simple self-deadlock |
| |
On Thu, Feb 02, 2012 at 11:56:38AM -0800, Josh Triplett wrote: > On Thu, Feb 02, 2012 at 08:20:17AM -0800, Paul E. McKenney wrote: > > On Wed, Feb 01, 2012 at 04:55:54PM -0800, Josh Triplett wrote: > > > On Wed, Feb 01, 2012 at 11:41:21AM -0800, Paul E. McKenney wrote: > > > > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> > > > > > > > > It is illegal to have a grace period within a same-flavor RCU read-side > > > > critical section, so this commit adds lockdep-RCU checks to splat when > > > > such abuse is encountered. This commit does not detect more elaborate > > > > RCU deadlock situations. These situations might be a job for lockdep > > > > enhancements. > > > > > > Since doing so also violates the prohibition on blocking within an RCU > > > read-side critical section, wouldn't it suffice to call might_sleep() or > > > equivalent, which also detects other problems? (Obviously this doesn't > > > apply to SRCU, but it applies to the other variants of RCU.) > > > > Yes, but... > > > > The advantage of the lockdep-RCU splat is that it gives you a better > > hint as to where the RCU read-side critical section was entered, which > > is very helpful when tracking these down, especially when they are > > intermittent. > > Ah, fair enough. > > > And yes, I should also well check for the other variants of RCU read-side > > critical section (other than RCU). Done. > > Oh? What hadn't you checked for?
Things like synchronize_sched() in rcu_read_lock() critical section and vice versa.
> > I also glued the strings together to promote grepability as you suggest > > later. (But I leave it to you to get checkpatch.pl upgraded -- it currently > > warns about long lines, but not about strings split across lines.) > > It theoretically shouldn't warn about long lines that consist only of a > quoted string possibly followed by ',' or ');'; it has a check to ignore > those. After you glued the strings together, what did you end up with?
You are quite right -- it ignores the lines with long strings.
> As for adding a warning about strings broken across lines, that seems > sensible. Some quick grepping suggests that doing so would catch a pile > of existing code, too. Patch to follow momentarily.
Indeed, I might not be the only one to overgeneralize from the 80-character warning. ;-)
Thanx, Paul
| |