Messages in this thread | | | Date | Tue, 19 Dec 2017 17:46:19 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] lockdep: Show up to three levels for a deadlock scenario |
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On Tue, Dec 19, 2017 at 11:30:29AM -0500, Dhaval Giani wrote: > On 2017-12-14 12:59 PM, Peter Zijlstra wrote: > > On Thu, Dec 14, 2017 at 12:38:52PM -0500, Steven Rostedt wrote: > >> > >> Currently, when lockdep detects a possible deadlock scenario that involves 3 > >> or more levels, it just shows the chain, and a CPU sequence order of the > >> first and last part of the scenario, leaving out the middle level and this > >> can take a bit of effort to understand. By adding a third level, it becomes > >> easier to see where the deadlock is. > > > > So is anybody actually using this? This (together with the callchain for > > #0) is always the first thing of the lockdep output I throw away. > > > > Yes :-). The other stuff is unreadable to people not you.
It really isn't that hard, Its mostly a question of TL;DR.
#0 is useless and should be thrown out #1 shows where we take #1 while holding #0 .. #n shows where we take #n while holding #n-1
And the bottom callstack shows where we take #0 while holding #n. Which gets you a nice circle in your graph, which spells deadlock.
Plenty people have shown they get this stuff.
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