On Mon, Apr 28, 2014 at 3:24 AM, Daniel Thompson <daniel.thomp...@linaro.org> wrote: > On 25/04/14 17:45, Steven Rostedt wrote: >> On Fri, 25 Apr 2014 17:29:22 +0100 >> Daniel Thompson <daniel.thomp...@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. > >
One of the advantages of FIQ debugger is that it can be triggered from an FIQ (NMI for those in x86 land), and Jason and I have discussed using FIQs for kgdb to allow interrupting cpus stuck in critical sections. If that gets implemented the above assumption will no longer be correct. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
