* perf record --kcore does not work when /proc/modules changed during copy
@ 2022-09-02 15:46 Daniel Dao
2022-09-02 16:08 ` Adrian Hunter
0 siblings, 1 reply; 2+ messages in thread
From: Daniel Dao @ 2022-09-02 15:46 UTC (permalink / raw)
To: acme, linux-perf-users, kernel-team, linux-kernel, jolsa,
adrian.hunter, namhyung
Hi Perf tools maintainers,
`perf record --kcore` frequently did not work on a somewhat busy system.
For example:
sudo perf record --kcore -- sleep 1
ERROR: Failed to copy kcore
Using strace to look at the invocation, the failure looks like:
...
openat(AT_FDCWD, "/proc/modules", O_RDONLY) = 56
openat(AT_FDCWD, "perf.data/kcore_dir/modules", O_RDONLY) = 57
read(56, "mpls_gso 16384 0 - Live 0xffffff"..., 4096) = 4070
read(57, "mpls_gso 16384 0 - Live 0xffffff"..., 4070) = 4070
read(56, "xt_conntrack 24576 22 - Live 0xf"..., 4096) = 3738
read(57, "xt_conntrack 24576 22 - Live 0xf"..., 3738) = 3738
close(57) = 0
close(56) = 0
close(55) = 0
unlink("perf.data/kcore_dir/kcore") = 0
close(54) = 0
unlink("perf.data/kcore_dir/modules") = 0
unlink("perf.data/kcore_dir/kallsyms") = 0
write(2, "ERROR: Failed to copy kcore\n", 28ERROR: Failed to copy kcore
...
We can see that the verification of proc/modules failed because /proc/modules
output changed after we copied kcore. When i looked at it, they are caused by
changes of module refcount which seems expected on busy systems, such as
< tcp_bbr 40960 12644 - Live 0x0000000000000000
---
> tcp_bbr 40960 12678 - Live 0x0000000000000000
Any suggestions on how to make this work is much appreciated.
Cheers,
Daniel.
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: perf record --kcore does not work when /proc/modules changed during copy
2022-09-02 15:46 perf record --kcore does not work when /proc/modules changed during copy Daniel Dao
@ 2022-09-02 16:08 ` Adrian Hunter
0 siblings, 0 replies; 2+ messages in thread
From: Adrian Hunter @ 2022-09-02 16:08 UTC (permalink / raw)
To: Daniel Dao, acme, linux-perf-users, kernel-team, linux-kernel,
jolsa, namhyung
On 2/09/22 18:46, Daniel Dao wrote:
> Hi Perf tools maintainers,
>
> `perf record --kcore` frequently did not work on a somewhat busy system.
> For example:
>
> sudo perf record --kcore -- sleep 1
> ERROR: Failed to copy kcore
>
> Using strace to look at the invocation, the failure looks like:
>
> ...
> openat(AT_FDCWD, "/proc/modules", O_RDONLY) = 56
> openat(AT_FDCWD, "perf.data/kcore_dir/modules", O_RDONLY) = 57
> read(56, "mpls_gso 16384 0 - Live 0xffffff"..., 4096) = 4070
> read(57, "mpls_gso 16384 0 - Live 0xffffff"..., 4070) = 4070
> read(56, "xt_conntrack 24576 22 - Live 0xf"..., 4096) = 3738
> read(57, "xt_conntrack 24576 22 - Live 0xf"..., 3738) = 3738
> close(57) = 0
> close(56) = 0
> close(55) = 0
> unlink("perf.data/kcore_dir/kcore") = 0
> close(54) = 0
> unlink("perf.data/kcore_dir/modules") = 0
> unlink("perf.data/kcore_dir/kallsyms") = 0
> write(2, "ERROR: Failed to copy kcore\n", 28ERROR: Failed to copy kcore
> ...
>
> We can see that the verification of proc/modules failed because /proc/modules
> output changed after we copied kcore. When i looked at it, they are caused by
> changes of module refcount which seems expected on busy systems, such as
>
> < tcp_bbr 40960 12644 - Live 0x0000000000000000
> ---
> > tcp_bbr 40960 12678 - Live 0x0000000000000000
>
> Any suggestions on how to make this work is much appreciated.
At the moment I can't think why the proc/modules file needs to be
compared at all since we also compare proc/kallsyms which should be
enough.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2022-09-02 16:08 ` Adrian Hunter
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