| Date | Mon, 28 Apr 2014 11:24:26 +0100 | From | Daniel Thompson <> | Subject | Re: [RFC v3 1/9] sysrq: Implement __handle_sysrq_nolock to avoid recursive locking in kdb |
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On 25/04/14 17:45, Steven Rostedt wrote: > On Fri, 25 Apr 2014 17:29:22 +0100 > Daniel Thompson <daniel.thompson@linaro.org> wrote: > >> If kdb is triggered using SysRq-g then any use of the sr command results >> in the SysRq key table lock being recursively acquired, killing the debug >> session. That patch resolves the problem by introducing a _nolock >> alternative for __handle_sysrq. >> >> Strictly speaking this approach risks racing on the key table when kdb is >> triggered by something other than SysRq-g however in that case any other >> CPU involved should release the spin lock before kgdb parks the slave >> CPUs. > > Is that case documented somewhere in the code comments?
Perhaps not near enough to the _nolock but the primary bit of comment is here (and in same file as kdb_sr). --- cut here --- * kdb_main_loop - After initial setup and assignment of the * controlling cpu, all cpus are in this loop. One cpu is in * control and will issue the kdb prompt, the others will spin * until 'go' or cpu switch. --- cut here ---
The mechanism kgdb uses to quiesce other CPUs means other CPUs cannot be in irqsave critical sections.
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