Re: [PATCH] sched/psi: initialize *flags in psi_memstall_enter when PSI is disabled

[Johannes Weiner]

On Sun, Apr 05, 2026 at 01:50:44PM +0800, Mashiro Chen wrote:
> When PSI is disabled, psi_memstall_enter() returns early without
> writing to *flags, leaving the caller's local variable uninitialized.
> psi_memstall_leave() also returns early when PSI is disabled and does
> not read *flags, so the uninitialized value is never used functionally.
>
> However, KMSAN tracks the shadow and origin metadata per physical
> address. When a kernel stack page is subsequently reused, a new object
> at the same address inherits the stale KMSAN shadow from the old
> uninitialized pflags, causing spurious uninit-value reports in
> unrelated code paths such as __flush_smp_call_function_queue().
>
> Initialize *flags to 0 in the psi_disabled early-return path to
> prevent the stale shadow from escaping the callers' stack frames.

How is this not a kmsan bug?

I don't think putting an unexpected init into unrelated code with no
comment is an appropriate fix for what seems like a false positive in
this tool.