linux-kernel - Re: [PATCH AUTOSEL 5.4 30/73] futex: Fix inode life-time issue

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Date:   Mon, 23 Mar 2020 20:18:04 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Sasha Levin <sashal@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable <stable@...r.kernel.org>
Cc:     kernel list <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH AUTOSEL 5.4 30/73] futex: Fix inode life-time issue

On Wed, Mar 18, 2020 at 9:54 PM Sasha Levin <sashal@...nel.org> wrote:
>
> From: Peter Zijlstra <peterz@...radead.org>
>
> [ Upstream commit 8019ad13ef7f64be44d4f892af9c840179009254 ]
>
> As reported by Jann, ihold() does not in fact guarantee inode
> persistence. And instead of making it so, replace the usage of inode
> pointers with a per boot, machine wide, unique inode identifier.
>
> This sequence number is global, but shared (file backed) futexes are
> rare enough that this should not become a performance issue.

Please also take this patch, together with
8d67743653dce5a0e7aa500fcccb237cde7ad88e "futex: Unbreak futex
hashing", into the older stable branches. This has to go all the way
back; as far as I can tell, the bug already existed at the beginning
of git history.