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Date: Tue, 10 Apr 2012 09:14:51 -0600
From: David Ahern <dsahern@gmail.com>
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To: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>
CC: mingo@redhat.com, acme@ghostprotocols.net, a.p.zijlstra@chello.nl,
        paulus@samba.org, fweisbec@gmail.com, eranian@google.com,
        linux-kernel@vger.kernel.org
Subject: Re: [BUG PATCH] perf: kvm - finding struct machine fails for PERF_RECORD_MMAP
References: <20120409081835.10576.22018.stgit@abhimanyu.in.ibm.com> <4F8369E6.5090608@gmail.com> <87iph8xnim.fsf@abhimanyu.in.ibm.com>
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On 4/9/12 9:40 PM, Nikunj A Dadhania wrote:
> I can think of two places where it can happen:
>
> 1) perf_event__synthesize_kernel_mmap
>
>          [...]
>   	mmap_name = machine__mmap_name(machine, name_buff, sizeof(name_buff));
> 	if (machine__is_host(machine)) {
>             ...
> 	} else {
> 		event->header.misc = PERF_RECORD_MISC_GUEST_KERNEL;
> 		if (machine__is_default_guest(machine))
> 			filename = (char *) symbol_conf.default_guest_kallsyms;
> 		else {
> 			sprintf(path, "%s/proc/kallsyms", machine->root_dir);
> 			filename = path;
> 		}
> 	}
>          [...]
> 	event->mmap.header.type = PERF_RECORD_MMAP;
>          [...]
>          event->mmap.pid   = machine->pid;
>
> 2) perf_event__synthesize_modules
>
>          [...]
> 	if (machine__is_host(machine))
> 		event->header.misc = PERF_RECORD_MISC_KERNEL;
> 	else
> 		event->header.misc = PERF_RECORD_MISC_GUEST_KERNEL;
>          [...]
> 	event->mmap.header.type = PERF_RECORD_MMAP;
>          [...]
>          event->mmap.pid   = machine->pid;
>
> BTW, i am testing this on latest -tip(498c911).
>
> In my case, I am able to recreate this everytime. And have verified that
> the event->header.type that I hit here is of type PERF_RECORD_MMAP.

I was thinking runtime, not initialization. Adding -o direct_io to the 
sshfs mount did the trick. Reading guest /proc files exposes the segfault.

David