RE: x86/kprobes: kretprobe fails to triggered if kprobe at function entry is not optimized (trigger by int3 breakpoint)

[Eddy_Wu@xxxxxxxxxxxxxx]

> -----Original Message-----
> From: peterz@xxxxxxxxxxxxx <peterz@xxxxxxxxxxxxx>
> Sent: Tuesday, August 25, 2020 8:09 PM
> To: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Cc: Eddy Wu (RD-TW) <Eddy_Wu@xxxxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; x86@xxxxxxxxxx; David S. Miller
> <davem@xxxxxxxxxxxxx>
> Subject: Re: x86/kprobes: kretprobe fails to triggered if kprobe at function entry is not optimized (trigger by int3 breakpoint)
>
> Surely we can do a lockless list for this. We have llist_add() and
> llist_del_first() to make a lockless LIFO/stack.
>

llist operations require atomic cmpxchg, for some arch doesn't have CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG, in_nmi() check might still needed.
(HAVE_KRETPROBES && !CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG): arc, arm, csky, mips

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