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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Calvin Owens <calvin@wbinvd.org>
Cc: linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org,
	"Lai, Yi" <yi1.lai@linux.intel.com>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>, x86@kernel.org
Subject: Re: [tip: locking/urgent] futex: Allow to resize the private local
 hash
Message-ID: <20250617095037.sOnrJlPX@linutronix.de>
References: <20250602110027.wfqbHgzb@linutronix.de>
 <174965275618.406.11364856155202390038.tip-bot2@tip-bot2>
 <aFBQ8CBKmRzEqIfS@mozart.vkv.me>
 <20250617071628.lXtqjG7C@linutronix.de>
 <aFEz_Fzr-_-nGAHV@mozart.vkv.me>
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In-Reply-To: <aFEz_Fzr-_-nGAHV@mozart.vkv.me>

On 2025-06-17 02:23:08 [-0700], Calvin Owens wrote:
> Ugh, I'm sorry, I was in too much of a hurry this morning... cargo is
> obviously not calling PR_FUTEX_HASH which is new in 6.16 :/
No worries.

> > This is with LTO enabled.
>=20
> Full lto with llvm-20.1.7.
>=20
=E2=80=A6
> Nothing showed up in the logs but the RCU stalls on CPU16, always in
> queued_spin_lock_slowpath().
>=20
> I'll run the build it was doing when it happened in a loop overnight and
> see if I can trigger it again.

Please check if you can reproduce it and if so if it also happens
without lto.
I have no idea why one spinlock_t remains locked. It is either locked or
some stray memory.

Oh. Lockdep adds quite some overhead but it should complain that a
spinlock_t is still locked while returning to userland.

> > > Thanks,
> > > Calvin
> >=20
Sebastian