On Thu, 28 Jan 2021 00:13:53 +0900
Masami Hiramatsu <mhira...@kernel.org> wrote:
> Hi Nikolay,
>
> On Wed, 27 Jan 2021 15:43:29 +0200
> Nikolay Borisov <nbori...@suse.com> wrote:
>
> > Hello,
> >
> > I'm currently seeing latest Linus' master being somewhat broken w.r.t
> > krpobes. In particular I have the following test-case:
> >
> > #!/bin/bash
> >
> > mkfs.btrfs -f /dev/vdc &> /dev/null
> > mount /dev/vdc /media/scratch/
> >
> > bpftrace -e 'kprobe:btrfs_sync_file {printf("kprobe: %s\n", kstack());}'
> > &>bpf-output &
> > bpf_trace_pid=$!
> >
> > # force btrfs_sync_file to be called
> > sleep 2
> > xfs_io -f -c "pwrite 0 4m" -c "fsync" /media/scratch/file5
> >
> > kill $bpf_trace_pid
> > sleep 1
> >
> > grep -q kprobe bpf-output
> > retval=$?
> > rm -f bpf-output
> > umount /media/scratch
> >
> > exit $retval
> >
> > It traces btrfs_sync_file which is called when fsync is executed on a
> > btrfs file, however I don't see the stacktrace being printed i.e the
> > kprobe doesn't fire at all. The following alternative program:
> >
> > bpftrace -e 'tracepoint:btrfs:btrfs_sync_file {printf("tracepoint:
> > %s\n", kstack());} kprobe:btrfs_sync_file {printf("kprobe: %s\n",
> > kstack());}'
> >
> > only prints the stack from the tracepoint and not from the kprobe, given
> > that the tracepoint is called from the btrfs_sync_file function.
>
> Thank you for reporting!
>
> If you don't mind, could you confirm it with ftrace (tracefs)?
> bpftrace etc. involves too many things. It is better to test with
> simpler way to test it.
> I'm not familer with the bpftrace, but I think you can check it with
>
> # cd /sys/kernel/debug/tracing
> # echo p:myevent btrfs_sync_file >> kprobe_events
> # echo stacktrace > events/kprobes/myevent/trigger
> (or echo 1 > options/stacktrace , if trigger file doesn't exist)
Of course, also you have to enable the event.
# echo 1 > events/kprobes/myevent/enable
And check the results
# cat trace
> Could you also share your kernel config, so that we can reproduce it?
Thank you,
>
> >
> > I started bisecting this and arrived at the following commit:
> >
> > 0d00449c7a28 ("x86: Replace ist_enter() with nmi_enter()")
> >
> > FWIW the following series is applied on the kernel I was testing:
> > https://lore.kernel.org/lkml/159870598914.1229682.15230803449082078353.stgit@devnote2/
> >
> > but it's still broken.
>
> Peter, would you have any idea?
>
> Thank you,
>
> --
> Masami Hiramatsu <mhira...@kernel.org>
--
Masami Hiramatsu <mhira...@kernel.org>
