linux-kernel - Re: [PATCH v3 0/7] riscv: ftrace: atmoic patching and preempt improvements

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Message-ID: <87a5d9gq84.fsf@all.your.base.are.belong.to.us>
Date: Fri, 06 Dec 2024 09:39:23 +0100
From: Björn Töpel <bjorn@...nel.org>
To: Evgenii Shatokhin <e.shatokhin@...ro.com>, Andy Chiu <andybnac@...il.com>
Cc: Palmer Dabbelt <palmer@...belt.com>, Nathan Chancellor
 <nathan@...nel.org>, Justin Stitt <justinstitt@...gle.com>, Bill Wendling
 <morbo@...gle.com>, Nick Desaulniers <ndesaulniers@...gle.com>, Albert Ou
 <aou@...s.berkeley.edu>, Paul Walmsley <paul.walmsley@...ive.com>,
 linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
 llvm@...ts.linux.dev, bjorn@...osinc.com, puranjay12@...il.com,
 alexghiti@...osinc.com, yongxuan.wang@...ive.com, greentime.hu@...ive.com,
 nick.hu@...ive.com, nylon.chen@...ive.com, tommy.wu@...ive.com,
 eric.lin@...ive.com, viccent.chen@...ive.com, zong.li@...ive.com,
 samuel.holland@...ive.com
Subject: Re: [PATCH v3 0/7] riscv: ftrace: atmoic patching and preempt
 improvements

Evgenii Shatokhin <e.shatokhin@...ro.com> writes:

> On 03.12.2024 15:18, Björn Töpel wrote:
>> Andy!
>> 
>> "atomic" spelling in the Subject line.
>> 
>> Andy Chiu <andybnac@...il.com> writes:
>> 
>>> Changes in v3:
>>> - Add a fix tag for patch 1
>>> - Add a data fence before sending out remote fence.i (6)
>>> - Link to v2: https://lore.kernel.org/all/20240628-dev-andyc-dyn-ftrace-v4-v2-0-1e5f4cb1f049@sifive.com/
>> 
>> Hmm, the fixes tag was not included.
>> 
>> Also, there was a lot of comments from v2 that was not addressed:
>> 
>>   * Minor spelling nits
>>   * Breaking DIRECT_CALL, and include Puranjay's CALL_OPS work in the
>>     same series for DIRECT_CALL, to avoid breakage.
>
> Yes, FTRACE_WITH_DIRECT_CALLS is currently broken. If I try to insmod 
> samples/ftrace/ftrace-direct.ko, it reports a failure:
>
>
> [  179.531472] ------------[ ftrace bug ]------------
> [  179.531761] ftrace failed to modify
> [  179.531786] [<ffffffff8005f9ac>] wake_up_process+0x0/0x24
> [  179.532577]  actual:   97:e2:fa:ff:13:00:00:00
> [  179.533211] Setting ftrace call site to call ftrace function
> [  179.534409] ftrace record flags: 99980001
> [  179.534692]  (1)     tramp: ftrace_caller+0x0/0x34 
> (call_direct_funcs+0x0/0x14)
> [  179.534692]  expected tramp: ffffffff01b0d000
> ...

And just a regular Ubuntu 24.10 will fail with all subsystems using BPF
trampoline, e.g.
 ------------[ ftrace bug ]------------
 ftrace failed to modify
 [<ffffffff80250d98>] bpf_lsm_file_open+0x0/0x1c

CALL_OPS with definitely a must for this series.


Björn