interrupted single step fixes
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Cover letter [PATCH 0/3] interrupted single step fixes
Hi Pratyush,
Quoted 11 lines · Pratyush Anand
Quoted 6 lines · James Morse
Enable
CONFIG_SAMPLE_HW_BREAKPOINT, then:Quoted 2 lines
insmod data_breakpoint.ko ksym=__sysrq_enabled
cat/proc/sys/kernel/sysrqWith mainline you will hit the watchpoint forever, Pratyush's patches reduce this to ~10 times. These patches reduce that to the expected once.
So, when you say that it reduce to ~10 times with my patches, did you use all patches ie 1-4 or only 1-3. 1-3 is just the preparation and 4 was my actual solution. I had seen only once (which is expected) with all(1-4) of my patches.
Yes, your patches 1-3 were fixing <something> in perf to cause us to step the watchpoint, and 4&5 disabled/re-enabled IRQs in the interrupted context when we do the step.
Quoted 3 lines
In my understanding, you have used 1-3 of mine and then replaced my 4th patch with your patches in this series.If I understood correctly then, now we can handle IRQ between breakpoint and step handler, I think thats good.
For use with your example, yes, but I think these fix the existing hwbreakpoint/kgdb users. (unless none of this has ever worked?)
(I still haven't put together a test for kgdb)
Quoted 3 lines
Only concern
seems that how does this approach behave when we put a hardware breakpoint on a ISR called between breakpoint and step exception.
Yes, this won't work because the IRQ:breakpoint occurs while the debug hardware is already in use to step the first breakpoint. (but this only works today because we take breakpoints 10s of times)
It looks like this is an important use-case for perf... this is more complicated than just surviving an IRQ during single step.
I think ignore these patches, I'll try and come up with a way to get that 'nested' case working too. Will's suggestion of separating what we do for perf and user space may make this easier[0].
Thanks,
James