Re: [PATCH -tip v8 00/26] kprobes: introduce NOKPROBE_SYMBOL, bugfixes and scalbility efforts
From: Masami Hiramatsu
Date: Fri Mar 14 2014 - 09:11:35 EST
Ping? :)
(2014/03/05 20:58), Masami Hiramatsu wrote:
> Hi,
> Here is the version 8 of NOKPROBE_SYMBOL series.
>
> This just updates the kprobe_table hash entry size enlargement
> to 512 from 4096. That also includes decoupling the hash size
> of kprobes one from kretprobes one, since both has different
> hash-bases.
>
>
> Changes
> =======
>>From this series, I update 1 patch;
> - Enlarge kprobes hash table size to 512 instead of
> 4096.
> And evaluate the improvement again with new hash.
>
> Blacklist improvements
> ======================
> Currently, kprobes uses __kprobes annotation and internal symbol-
> name based blacklist to prohibit probing on some functions, because
> to probe those functions may cause an infinite recursive loop by
> int3/debug exceptions.
> However, current mechanisms have some problems especially from the
> view point of maintaining code;
> - __kprobes is easy to confuse the function is
> used by kprobes, despite it just means "no kprobe
> on it".
> - __kprobes moves functions to different section
> this will be not good for cache optimization.
> - symbol-name based solution is not good at all,
> since the symbol name easily be changed, and
> we cannot notice it.
> - it doesn't support functions in modules at all.
>
> Thus, I decided to introduce new NOKPROBE_SYMBOL macro for building
> an integrated kprobe blacklist.
>
> The new macro stores the address of the given symbols into
> _kprobe_blacklist section, and initialize the blacklist based on the
> address list at boottime.
> This is also applied for modules. When loading a module, kprobes
> finds the blacklist symbols in _kprobe_blacklist section in the
> module automatically.
> This series replaces all __kprobes on x86 and generic code with the
> NOKPROBE_SYMBOL() too.
>
> Although, the new blacklist still support old-style __kprobes by
> decoding .kprobes.text if exist, because it still be used on arch-
> dependent code except for x86.
>
> Scalability effort
> ==================
> This series fixes not only the kernel crashable "qualitative" bugs
> but also "quantitative" issue with massive multiple kprobes. Thus
> we can now do a stress test, putting kprobes on all (non-blacklisted)
> kernel functions and enabling all of them.
> To set kprobes on all kernel functions, run the below script.
> ----
> #!/bin/sh
> TRACE_DIR=/sys/kernel/debug/tracing/
> echo > $TRACE_DIR/kprobe_events
> grep -iw t /proc/kallsyms | tr -d . | \
> awk 'BEGIN{i=0};{print("p:"$3"_"i, "0x"$1); i++}' | \
> while read l; do echo $l >> $TRACE_DIR/kprobe_events ; done
> ----
> Since it doesn't check the blacklist at all, you'll see many write
> errors, but no problem :).
>
> Note that a kind of performance issue is still in the kprobe-tracer
> if you trace all functions. Since a few ftrace functions are called
> inside the kprobe tracer even if we shut off the tracing (tracing_on
> = 0), enabling kprobe-events on the functions will cause a bad
> performance impact (it is safe, but you'll see the system slowdown
> and no event recorded because it is just ignored).
> To find those functions, you can use the third column of
> (debugfs)/tracing/kprobe_profile as below, which tells you the number
> of miss-hit(ignored) for each events. If you find that some events
> which have small number in 2nd column and large number in 3rd column,
> those may course the slowdown.
> ----
> # sort -rnk 3 (debugfs)/tracing/kprobe_profile | head
> ftrace_cmp_recs_4907 264950231 33648874543
> ring_buffer_lock_reserve_5087 0 4802719935
> trace_buffer_lock_reserve_5199 0 4385319303
> trace_event_buffer_lock_reserve_5200 0 4379968153
> ftrace_location_range_4918 18944015 2407616669
> bsearch_17098 18979815 2407579741
> ftrace_location_4972 18927061 2406723128
> ftrace_int3_handler_1211 18926980 2406303531
> poke_int3_handler_199 18448012 1403516611
> inat_get_opcode_attribute_16941 0 12715314
> ----
>
> I'd recommend you to enable events on such functions after all other
> events enabled. Then its performance impact becomes minimum.
>
> To enable kprobes on all kernel functions, run the below script.
> ----
> #!/bin/sh
> TRACE_DIR=/sys/kernel/debug/tracing
> echo "Disable tracing to remove tracing overhead"
> echo 0 > $TRACE_DIR/tracing_on
>
> BADS="ftrace_cmp_recs ring_buffer_lock_reserve trace_buffer_lock_reserve trace_event_buffer_lock_reserve ftrace_location_range bsearch ftrace_location ftrace_int3_handler poke_int3_handler inat_get_opcode_attribute"
> HIDES=
> for i in $BADS; do HIDES=$HIDES" --hide=$i*"; done
>
> SDATE=`date +%s`
> echo "Enabling trace events: start at $SDATE"
>
> cd $TRACE_DIR/events/kprobes/
> for i in `ls $HIDES` ; do echo 1 > $i/enable; done
> for j in $BADS; do for i in `ls -d $j*`;do echo 1 > $i/enable; done; done
>
> EDATE=`date +%s`
> TIME=`expr $EDATE - $SDATE`
> echo "Elapsed time: $TIME"
> ----
> Note: Perhaps, using systemtap doesn't need to consider above bad
> symbols since it has own logic not to probe itself.
>
> Result
> ======
> These were also enabled after all other events are enabled.
> And it took 2254 sec(without any intervals) for enabling 37222 probes.
> And at that point, the perf top showed below result:
> ----
> Samples: 10K of event 'cycles', Event count (approx.): 270565996
> + 16.39% [kernel] [k] native_load_idt
> + 11.17% [kernel] [k] int3
> - 7.91% [kernel] [k] 0x00007fffa018e8e0
> - 0xffffffffa018d8e0
> 59.09% trace_event_buffer_lock_reserve
> kprobe_trace_func
> kprobe_dispatcher
> + 40.45% trace_event_buffer_lock_reserve
> ----
> 0x00007fffa018e8e0 may be the trampoline buffer of an optimized
> probe on trace_event_buffer_lock_reserve. native_load_idt and int3
> are also called from normal kprobes.
> This means, at least my environment, kprobes now passed the
> stress test, and even if we put probes on all available functions
> it just slows down about 50%.
>
> Changes from v7:
> - [24/26] Enlarge hash table to 512 instead of 4096.
> - Re-evaluate the performance improvements.
>
> Changes from v6:
> - Updated patches on the latest -tip.
> - [1/26] Add patch: Fix page-fault handling logic on x86 kprobes
> - [2/26] Add patch: Allow to handle reentered kprobe on singlestepping
> - [9/26] Add new patch: Call exception_enter after kprobes handled
> - [12/26] Allow probing fetch functions in trace_uprobe.c.
> - [24/26] Add new patch: Enlarge kprobes hash table size
> - [25/26] Add new patch: Kprobe cache for frequently accessd kprobes
> - [26/26] Add new patch: Skip Ftrace hlist check with ftrace-based kprobe
>
> Changes from v5:
> - [2/22] Introduce nokprobe_inline macro
> - [6/22] Prohibit probing on memset/memcpy
> - [11/22] Allow probing on text_poke/hw_breakpoint
> - [12/22] Use nokprobe_inline macro instead of __always_inline
> - [14/22] Ditto.
> - [21/22] Remove preempt disable/enable from kprobes/x86
> - [22/22] Add emergency int3 recovery code
>
> Thank you,
>
> ---
>
> Masami Hiramatsu (26):
> [BUGFIX]kprobes/x86: Fix page-fault handling logic
> kprobes/x86: Allow to handle reentered kprobe on singlestepping
> kprobes: Prohibit probing on .entry.text code
> kprobes: Introduce NOKPROBE_SYMBOL() macro for blacklist
> [BUGFIX] kprobes/x86: Prohibit probing on debug_stack_*
> [BUGFIX] x86: Prohibit probing on native_set_debugreg/load_idt
> [BUGFIX] x86: Prohibit probing on thunk functions and restore
> kprobes/x86: Call exception handlers directly from do_int3/do_debug
> x86: Call exception_enter after kprobes handled
> kprobes/x86: Allow probe on some kprobe preparation functions
> kprobes: Allow probe on some kprobe functions
> ftrace/*probes: Allow probing on some functions
> x86: Allow kprobes on text_poke/hw_breakpoint
> x86: Use NOKPROBE_SYMBOL() instead of __kprobes annotation
> kprobes: Use NOKPROBE_SYMBOL macro instead of __kprobes
> ftrace/kprobes: Use NOKPROBE_SYMBOL macro in ftrace
> notifier: Use NOKPROBE_SYMBOL macro in notifier
> sched: Use NOKPROBE_SYMBOL macro in sched
> kprobes: Show blacklist entries via debugfs
> kprobes: Support blacklist functions in module
> kprobes: Use NOKPROBE_SYMBOL() in sample modules
> kprobes/x86: Use kprobe_blacklist for .kprobes.text and .entry.text
> kprobes/x86: Remove unneeded preempt_disable/enable in interrupt handlers
> kprobes: Enlarge hash table to 512 entries
> kprobes: Introduce kprobe cache to reduce cache misshits
> ftrace: Introduce FTRACE_OPS_FL_SELF_FILTER for ftrace-kprobe
>
>
> Documentation/kprobes.txt | 24 +
> arch/Kconfig | 10
> arch/x86/include/asm/asm.h | 7
> arch/x86/include/asm/kprobes.h | 2
> arch/x86/include/asm/traps.h | 2
> arch/x86/kernel/alternative.c | 3
> arch/x86/kernel/apic/hw_nmi.c | 3
> arch/x86/kernel/cpu/common.c | 4
> arch/x86/kernel/cpu/perf_event.c | 3
> arch/x86/kernel/cpu/perf_event_amd_ibs.c | 3
> arch/x86/kernel/dumpstack.c | 9
> arch/x86/kernel/entry_32.S | 33 --
> arch/x86/kernel/entry_64.S | 20 -
> arch/x86/kernel/hw_breakpoint.c | 5
> arch/x86/kernel/kprobes/core.c | 162 ++++----
> arch/x86/kernel/kprobes/ftrace.c | 19 +
> arch/x86/kernel/kprobes/opt.c | 32 +-
> arch/x86/kernel/kvm.c | 4
> arch/x86/kernel/nmi.c | 18 +
> arch/x86/kernel/paravirt.c | 6
> arch/x86/kernel/traps.c | 35 +-
> arch/x86/lib/thunk_32.S | 3
> arch/x86/lib/thunk_64.S | 3
> arch/x86/mm/fault.c | 28 +
> include/asm-generic/vmlinux.lds.h | 9
> include/linux/compiler.h | 2
> include/linux/ftrace.h | 3
> include/linux/kprobes.h | 23 +
> include/linux/module.h | 5
> kernel/kprobes.c | 607 +++++++++++++++++++++---------
> kernel/module.c | 6
> kernel/notifier.c | 22 +
> kernel/sched/core.c | 7
> kernel/trace/ftrace.c | 3
> kernel/trace/trace_event_perf.c | 5
> kernel/trace/trace_kprobe.c | 66 ++-
> kernel/trace/trace_probe.c | 65 ++-
> kernel/trace/trace_probe.h | 15 -
> kernel/trace/trace_uprobe.c | 20 -
> samples/kprobes/jprobe_example.c | 1
> samples/kprobes/kprobe_example.c | 3
> samples/kprobes/kretprobe_example.c | 2
> 42 files changed, 824 insertions(+), 478 deletions(-)
>
> --
> Masami HIRAMATSU
> IT Management Research Dept. Linux Technology Center
> Hitachi, Ltd., Yokohama Research Laboratory
> E-mail: masami.hiramatsu.pt@xxxxxxxxxxx
>
>
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--
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@xxxxxxxxxxx
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