linux-kernel - Re: [tip: locking/urgent] futex: Allow to resize the private local hash

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Message-ID: <20250611144302.1MtYItK6@linutronix.de>
Date: Wed, 11 Jun 2025 16:43:02 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: linux-kernel@...r.kernel.org
Cc: linux-tip-commits@...r.kernel.org, "Lai, Yi" <yi1.lai@...ux.intel.com>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org
Subject: Re: [tip: locking/urgent] futex: Allow to resize the private local
 hash

On 2025-06-11 14:39:16 [-0000], tip-bot2 for Sebastian Andrzej Siewior wrote:
> The following commit has been merged into the locking/urgent branch of tip:
> 
> Commit-ID:     703b5f31aee5bda47868c09a3522a78823c1bb77
> Gitweb:        https://git.kernel.org/tip/703b5f31aee5bda47868c09a3522a78823c1bb77
> Author:        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> AuthorDate:    Mon, 02 Jun 2025 13:00:27 +02:00
> Committer:     Peter Zijlstra <peterz@...radead.org>
> CommitterDate: Wed, 11 Jun 2025 16:26:44 +02:00
> 
> futex: Allow to resize the private local hash
> 
> Once the global hash is requested there is no way back to switch back to
> the per-task private hash. This is checked at the begin of the function.
> 
> It is possible that two threads simultaneously request the global hash
> and both pass the initial check and block later on the
> mm::futex_hash_lock. In this case the first thread performs the switch
> to the global hash. The second thread will also attempt to switch to the
> global hash and while doing so, accessing the nonexisting slot 1 of the
> struct futex_private_hash.
> This has been reported by Yi Lai.
> 
> Verify under mm_struct::futex_phash that the global hash is not in use.

Could you please replace it with
	https://lore.kernel.org/all/20250610104400.1077266-5-bigeasy@linutronix.de/

It also looks like the subject from commit bd54df5ea7cad ("futex: Allow
to resize the private local hash")

Sebastian