On Thu, Apr 12, 2018 at 07:09:54PM -0500, Kim Phillips wrote: > On Thu, 12 Apr 2018 10:57:56 +0900 > Namhyung Kim <namhy...@kernel.org> wrote: > > > On Wed, Apr 11, 2018 at 07:29:40PM -0500, Kim Phillips wrote: > > > On Thu, 12 Apr 2018 08:31:09 +0900 > > > Namhyung Kim <namhy...@kernel.org> wrote: > > > > overflow can create it.. could you please show me the mmap event? > > > > > > > > $ perf script --show-mmap-events > > > > > > Here you go: > > > > > > swapper 0 [000] 0.000000: PERF_RECORD_MMAP -1/0: > > > [0xffff200008080000(0xdffff7f7ffff) @ 0xffff200008080000]: x > > > [kernel.kallsyms]_text > > > > 0xffff200008080000 > > + 0xdffff7f7ffff > > -------------------- > > 0xffffffffffffffff > > > > So it should have ~0ULL of the 'end' already. I don't know why it > > caused the problem.. Was it from the `perf.good`? > > There's no difference between the output of perf.good and perf.bad (the > difference between them is this reversion patch, .good being the one > that includes it).
Strange.. I have no idea what's the problem if the end is already ~0ULL then. > > > > swapper 0 [000] 0.000000: PERF_RECORD_MMAP -1/0: > > > [0xffff2000021e0000(0x18000) @ 0]: x > > > /lib/modules/4.16.0+/kernel/drivers/bus/arm-ccn.ko > > > > Hmm.. also it seems arm64 loads modules under the kernel. Then the > > fixup logic in machine__create_kernel_maps() won't work. Also as we > > you mean this: > > void __map_groups__fixup_end(struct map_groups *mg, enum map_type type) > ... > if (!curr->end) > curr->end = next->start; > > ? Right. For the fixup routine to work, a map should have 0 end. > Module symbol resolution is working, however. Maybe because this > 'paranoid' check was setting all the end addresses to ~0ULL? Only if the end was 0. Modules should have non-zero end. > Does the > design assume what maps__first() returns always has the lowest address, > and they're in sorted order? If so, what's the fix, to re-sort > map_groups afterwards? I think it's another problem but agree with you to fix it sorted. > > > don't use the map_groups__fixup_end() anymore > > ? I see map_groups__fixup_end() still being called. Oops, sorry. I looked a wrong branch (which I removed it but never sent to the LKML). > > > I think it's ok just checking the end address. > > Where? In machine__set_kernel_mmap(), like this reversion does? Yes, the reason is all other maps (i.e. modules) are already have non-zero end and we can fixup the end of kernel manually. > > The original commit says: > > The machine__set_kernel_mmap() is to setup addresses of the kernel map > using external info. But it has a check when the address is given from > an incorrect input which should have the start and end address of 0 > (i.e. machine__process_kernel_mmap_event). > > But we also use the end address of 0 for a valid input so change it to > check both start and end addresses. > > yet the comment above the code says: > > * Be a bit paranoid here, some perf.data file came with > * a zero sized synthesized MMAP event for the kernel. > > I tracked the first comment insertion down to this commit: > > commit 10fe12ef631a7e85022ed26304a37f033a6a95b8 > Author: Arnaldo Carvalho de Melo <a...@redhat.com> > Date: Sat Feb 20 19:53:13 2010 -0200 > > perf symbols: Fix up map end too on modular kernels with no modules > installed > > In 2161db9 we stopped failing when not finding modules when > asked too, but then the kernel maps (just one, for vmlinux) > wasn't having its ->end field correctly set up, so symbols were > not being found for the vmlinux map because its range was 0-0. > > which, when reading that last part, one would assume start == end == 0, > therefore size also == 0, the comment only talks about a zero *sized* > event...so did the original commit 1d12cec6ce99 "perf machine: Fix > paranoid check in machine__set_kernel_mmap()" really fix that case? > Because it checks start == 0, not necessarily the size... As I said I thought it only cares the start == end == 0 case and now the problem is fixed. So I added the start check for the fixup routine to take care of the end address. Otherwise kernel might have an overlap with some module(s). > > If not, can it be reverted until we figure out what's going on with > arm64? It's causing a regression in the meantime... I think the right solution would be 1. sort map groups 2. set kernel end to ~0ULL in machine__create_kernel_maps() 3. fix the kernel end to the start of next module (if any) manually instead of calling map_groups__fixup_end() Thanks, Namhyung
