On 7/10/2026 1:09 PM, Masami Hiramatsu wrote:

On Thu, 9 Jul 2026 14:22:25 +0000
Pu Hu [off-list ref] wrote:

quoted

From: Pu Hu <redacted>

A kprobe can be hit while another kprobe is in KPROBE_HIT_SS state. This
can happen when tracing or perf code runs from the debug exception path
while the first kprobe is preparing or executing its out-of-line
single-step instruction.

Currently arm64 treats a kprobe hit in KPROBE_HIT_SS as unrecoverable,
the same as a hit in KPROBE_REENTER. This is too strict. A hit in
KPROBE_HIT_SS is still a one-level reentry and can be handled by saving
the current kprobe state and setting up single-step for the new probe,
just like reentry from KPROBE_HIT_ACTIVE or KPROBE_HIT_SSDONE.

The truly unrecoverable case is hitting another kprobe while already in
KPROBE_REENTER, because the reentry save area has already been consumed.

Move KPROBE_HIT_SS to the recoverable reentry cases and leave
KPROBE_REENTER as the unrecoverable nested reentry case.

This mirrors the x86 fix in commit 6a5022a56ac3
("kprobes/x86: Allow to handle reentered kprobe on single-stepping").

Hi, as Sashiko commented, we have to save the saved_irqflag to
prev_kprobbe.

https://sashiko.dev/#/patchset/20260709142215.226872-1-hupu%40transsion.com?part=2

Thank you,

Hi Masami,

We already added the saved_irqflag support in Patch 3 of this series:

   arm64: kprobes: Save and restore saved_irqflag in prev_kprobe

However, I see the issue. Patch 2 and Patch 3 are separate commits,
so Patch 2 alone is not bisectable. I'll prepare a v3 that folds them
together, so the reentry logic and the saved_irqflag preservation land
in a single commit.

Thanks for pointing this out.

Thanks,
Pu Hu