linux-kernel - Re: [PATCHv2 0/8] hw_breakpoint: Breakpoint modification fixes and new modify ioctl

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Message-ID: <20180312112041.p6pksk7yj5nhbtju@gmail.com>
Date:   Mon, 12 Mar 2018 12:20:41 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        David Ahern <dsahern@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Milind Chabbi <chabbi.milind@...il.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Hari Bathini <hbathini@...ux.vnet.ibm.com>,
        Jin Yao <yao.jin@...ux.intel.com>,
        Kan Liang <kan.liang@...el.com>,
        Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
        Oleg Nesterov <onestero@...hat.com>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCHv2 0/8] hw_breakpoint: Breakpoint modification fixes and
 new modify ioctl


* Jiri Olsa <jolsa@...nel.org> wrote:

> hi,
> Milind Chabbi introduced new ioctl interface to change
> live breakpoint [1]. It allows to change its bp_addr,
> bp_len and bp_type throught new ioctl for perf breakpoint
> event.
> 
> We already have a kernel interface for this via 
> modify_user_hw_breakpoint function. This function however
> does not update the breakpoint slot counts.
> 
> So when the same functionality was exposed to user space
> (Milind's change), with simple test program I could put wrong
> slots count on arm server [2] and ended up with no breakpoints
> available on the system. Note it's not an issue on x86, because
> it shares slot single counter for both data and inst types
> (CONFIG_HAVE_MIXED_BREAKPOINTS_REGS).
> 
> This patchset contains my fixes for keeping breakpoint slots
> count updated. On top of it there's Milind's change for new
> _IOC_MODIFY_ATTRIBUTES ioctl interface to change a breakpoint.
> 
> As I mentioned above there're kernel users of
> modify_user_hw_breakpoint function, all ptrace related
> AFAICS, which could got broken.. so cc-ing Oleg ;-)
> 
> I ran gdb and strace tests suites and got same amount of
> skip/fail tests as when I run them on unpatched machine,
> so I assume nothing new got broken.
> 
> It's also available in here:
>   https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
>   perf/bp
> 
> v2 changes:
>   - added check for the rest of the perf_event_attr fields
>     to be the same as for kernel event
>
> Jiri Olsa (7):
>       hw_breakpoint: Pass bp_type directly as find_slot_idx argument
>       hw_breakpoint: Pass bp_type argument to __reserve_bp_slot|__release_bp_slot
>       hw_breakpoint: Add modify_bp_slot function
>       hw_breakpoint: Factor out __modify_user_hw_breakpoint function
>       hw_breakpoint: Add perf_event_attr fields check in __modify_user_hw_breakpoint
>       perf/core: Move perf_event_attr::sample_max_stack into perf_copy_attr
>       perf tests: Add breakpoint accounting/modify test
> 
> Milind Chabbi (1):
>       perf/core: fast breakpoint modification via _IOC_MODIFY_ATTRIBUTES.
> 
>  include/linux/hw_breakpoint.h         |   7 +++++
>  include/uapi/linux/perf_event.h       |   2 ++
>  kernel/events/core.c                  |  53 +++++++++++++++++++++++++++++--
>  kernel/events/hw_breakpoint.c         | 115 ++++++++++++++++++++++++++++++++++++++++++++++++-------------------
>  tools/include/uapi/linux/perf_event.h |   2 ++
>  tools/perf/tests/Build                |   1 +
>  tools/perf/tests/bp_account.c         | 195 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  tools/perf/tests/builtin-test.c       |   4 +++
>  tools/perf/tests/tests.h              |   1 +
>  9 files changed, 344 insertions(+), 36 deletions(-)
>  create mode 100644 tools/perf/tests/bp_account.c

Sorry about the late response - I suppose we could try this feature, but the 
tooling patches don't apply anymore. Mind re-sending a merged version, on top of 
latest -tip or so?

Thanks,

	Ingo