Messages in this thread | | | Date | Thu, 29 Apr 2021 12:30:07 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH] RISC-V: insn: Use a raw spinlock to protect TEXT_POKE* |
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On Wed, 28 Apr 2021 23:17:13 -0700 Palmer Dabbelt <palmer@dabbelt.com> wrote:
> From: Palmer Dabbelt <palmerdabbelt@google.com> > > We currently use text_mutex to protect the fixmap sections from > concurrent callers. This is convienent for kprobes as the generic code > already holds text_mutex, but ftrace doesn't which triggers a lockdep > assertion. We could take text_mutex for ftrace, but the jump label > implementation (which is currently taking text_mutex) isn't explicitly > listed as being sleepable and it's called from enough places it seems > safer to just avoid sleeping. > > arm64 and parisc, the other two TEXT_POKE-style patching > implemnetations, already use raw spinlocks. abffa6f3b157 ("arm64: > convert patch_lock to raw lock") lays out the case for a raw spinlock as > opposed to a regular spinlock, and while I don't know of anyone using rt > on RISC-V I'm sure it'll eventually show up and I don't see any reason > to wait.
On x86 we use text_mutex for jump label and ftrace. I don't understand the issue here. The arm64 update was already using spin locks in the insn_write() function itself. riscv just makes sure that text_mutex is held.
It also looks like ftrace on riscv should also have text_mutex held whenever it modifies the code. Because I see this in arch/riscv/kernel/ftrace.c:
int ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex) { mutex_lock(&text_mutex); return 0; }
int ftrace_arch_code_modify_post_process(void) __releases(&text_mutex) { mutex_unlock(&text_mutex); return 0; }
Which should be getting called before and after respectively from when ftrace does its updates.
Can you show me the back trace of that lockdep splat?
-- Steve
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