Messages in this thread | | | From | Arnaldo Carvalho de Melo <> | Date | Mon, 10 Feb 2020 10:13:32 -0300 | Subject | Re: [PATCH 3/4] perf map: Set kmap->kmaps backpointer for main kernel map chunks |
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Em Thu, Feb 06, 2020 at 03:10:38PM +0530, Ravi Bangoria escreveu: > Hi Arnaldo, > > On 12/23/19 7:02 PM, Arnaldo Carvalho de Melo wrote: > > From: Arnaldo Carvalho de Melo <acme@redhat.com> > > > > When a map is create to represent the main kernel area (vmlinux) with > > map__new2() we allocate an extra area to store a pointer to the 'struct > > maps' for the kernel maps, so that we can access that struct when > > loading ELF files or kallsyms, as we will need to split it in multiple > > maps, one per kernel module or ELF section (such as ".init.text"). > > > > So when map->dso->kernel is non-zero, it is expected that > > map__kmap(map)->kmaps to be set to the tree of kernel maps (modules, > > chunks of the main kernel, bpf progs put in place via > > PERF_RECORD_KSYMBOL, the main kernel). > > > > This was not the case when we were splitting the main kernel into chunks > > for its ELF sections, which ended up making 'perf report --children' > > processing a perf.data file with callchains to trip on > > __map__is_kernel(), when we press ENTER to see the popup menu for main > > histogram entries that starts at a symbol in the ".init.text" ELF > > section, e.g.: > > > > - 8.83% 0.00% swapper [kernel.vmlinux].init.text [k] start_kernel > > start_kernel > > cpu_startup_entry > > do_idle > > cpuidle_enter > > cpuidle_enter_state > > intel_idle > > > > Fix it. > > perf top from perf/core has started crashing at __map__is_kernel(): > > (gdb) bt > #0 __map__is_kernel (map=<optimized out>) at util/map.c:935 > #1 0x000000000045551d in perf_event__process_sample (machine=0xbab8f8, > sample=0x7fffe5ffa6d0, evsel=0xba7570, event=0xbcac50, tool=0x7fffffff84e0) > at builtin-top.c:833 > #2 deliver_event (qe=<optimized out>, qevent=<optimized out>) at builtin-top.c:1192 > #3 0x000000000050b9fb in do_flush (show_progress=false, oe=0x7fffffff87e0) > at util/ordered-events.c:244 > #4 __ordered_events__flush (oe=oe@entry=0x7fffffff87e0, how=how@entry=OE_FLUSH__TOP, > timestamp=timestamp@entry=0) at util/ordered-events.c:323 > #5 0x000000000050c1b5 in __ordered_events__flush (timestamp=<optimized out>, > how=<optimized out>, oe=<optimized out>) at util/ordered-events.c:339 > #6 ordered_events__flush (how=OE_FLUSH__TOP, oe=0x7fffffff87e0) at util/ordered-events.c:341 > #7 ordered_events__flush (oe=oe@entry=0x7fffffff87e0, how=how@entry=OE_FLUSH__TOP) > at util/ordered-events.c:339 > #8 0x0000000000454e21 in process_thread (arg=0x7fffffff84e0) at builtin-top.c:1104 > #9 0x00007ffff7f2c4e2 in start_thread () from /lib64/libpthread.so.0 > #10 0x00007ffff76086d3 in clone () from /lib64/libc.so.6 > > I haven't debugged it much but seems like the actual patch that's causing the > crash is de90d513b246 ("perf map: Use map->dso->kernel + map__kmaps() in > map__kmaps()"). > > Did you face this / aware of it?
No, I wasn't aware of this, will check, getting back from vacations today, so may take some time,
- Arnaldo
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