Messages in this thread | | | Date | Tue, 28 Feb 2012 19:47:43 +0530 | From | Srikar Dronamraju <> | Subject | Re: [PATCH] uprobes/core: handle breakpoint and signal step exception. |
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* Ingo Molnar <mingo@elte.hu> [2012-02-28 14:52:51]:
> > * Srikar Dronamraju <srikar@linux.vnet.ibm.com> wrote: > > > > > Where possible, we check and skip singlestepping the > > > > breakpointed instructions. For now we skip single byte as > > > > well as few multibyte nop instructions. However this can > > > > be extended to other instructions too. > > > > > > Is this an optimization - allowing a NOP to be inserted for > > > easy probe insertion? > > > > Yes, Its an optimization by which we avoid singlestep > > exception. > > That would be nice to comment in the code - nowhere in the > 'skip' logic is this fact mentioned, and it's really useful > information to pretty much anyone reading the code. > > It's also a nice optimization, there's no need to obfuscate its > existence.
okay, Will add.
> > > > > + case DIE_INT3: > > > > + /* Run your handler here */ > > > > + if (uprobe_bkpt_notifier(regs)) > > > > + ret = NOTIFY_STOP; > > > > > > This comment looks somewhat out of place. > > > > > > Also, I have not noticed this in the first patch, but 'bkpt' is > > > not a standard way to refer to breakpoints: we either use > > > 'breakpoint' or 'bp'. > > > > This is again one of those things that I changed from bp to > > bkpt based on LKML feedback. I am okay to go back to bp. > > :-/ I can understand it somewhat, 'bp' also means other things. > > 'hwbp' is a common name - you could use 'swbp' which would pair > with that nicely? >
Okay. However most of these functions call are called from within uprobes.c and have a uprobe prefix. So there is enough context for people to link bp to breakpoint.
> > Correct - and that still isolates the arch code from the core > uprobes code. > > We could also introduce 'struct generic_arch_uprobe_task' and > embedd that inside arch_uprobe via a short field name, to make > it easy to access: ->gen.field or so. > > You can also leave it as-is for now, I'll reconsider how things > look like with the patch following these bits and then make a > new suggestion if I see a better way. >
Will leave this as-is for now and wait for your suggestions.
> > > > > +/* > > > > + * There could be threads that have hit the breakpoint and are entering the > > > > + * notifier code and trying to acquire the uprobes_treelock. The thread > > > > + * calling delete_uprobe() that is removing the uprobe from the rb_tree can > > > > + * race with these threads and might acquire the uprobes_treelock compared > > > > + * to some of the breakpoint hit threads. In such a case, the breakpoint hit > > > > + * threads will not find the uprobe. Hence wait till the current breakpoint > > > > + * hit threads acquire the uprobes_treelock before the uprobe is removed > > > > + * from the rbtree. > > > > > > Hm, the last sentence does not parse for me. (even if it's > > > correct English it might make sense to rephrase it to be clearer > > > what is meant.) > > > > > > > Would this be okay with you. > > > > The current unregistering thread waits till all other threads > > that have hit a breakpoint to acquire the uprobes_treelock > > before the uprobe is removed from the rbtree. > > s/is removed/are removed > > ? >
At a time, we are unregistering just one probe,(atleast for now.) Wondering if "before uprobes are remove from rbtree." sounds as if more than one uprobe is being removed at one instance.
> If yes then indeed this reads better. > > > [...] > > > > If the thread was not in the middle of a uprobe hit then we go > > through the regular signal handling. > > > > Since there is no way this thread can hit a uprobe once a > > thread has entered get_signal_to_deliver(kernel code), I dont > > see a reason to move it under relock: > > Ok, fair enough. > Okay,
-- Thanks and Regards Srikar
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