From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lamorak.hansenpartnership.com (lamorak.hansenpartnership.com [198.37.111.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 37CFA1426C; Wed, 2 Apr 2025 16:03:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.37.111.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743609809; cv=none; b=KwEnswl10YawXPILQQb7BZpSpxEQd8glgqyvkC7Ejqjajerqd6gdDOB/oZhj2vJ/RXLaEb4iR/tEdzQGsdy07GyLwZgUhMzhaijFu+g3SerURBVu7F3ijxS4O+jbVVVezUfElIYNxume7YAw9Yysjmomfjxq/pSurWAynnBszBg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743609809; c=relaxed/simple; bh=UmbDjmV41iJpK/EJnXsfeFsBC/DhjuGNfc4vxpFjimU=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=Nb+uZmt2jh8h9iQM7Ve/d5GC4gWcPDRV6l8LJ1WdUyry/WF42mbdaqZJAngehrE9zhEdLZDhqJ6gSC/EHFZ+qPFosgiR6BImmJZaz6C2CUadueogPqYwul/bXtpHtClb5kR5Tm5iq0Me9d6oXASbdng7veuYRx88bxvJTXvWArw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=HansenPartnership.com; spf=pass smtp.mailfrom=HansenPartnership.com; dkim=pass (1024-bit key) header.d=hansenpartnership.com header.i=@hansenpartnership.com header.b=DYmSwesW; arc=none smtp.client-ip=198.37.111.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=HansenPartnership.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=HansenPartnership.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=hansenpartnership.com header.i=@hansenpartnership.com header.b="DYmSwesW" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=hansenpartnership.com; s=20151216; t=1743609805; bh=UmbDjmV41iJpK/EJnXsfeFsBC/DhjuGNfc4vxpFjimU=; h=Message-ID:Subject:From:To:Date:In-Reply-To:References:From; b=DYmSwesWKd+IOCe35ErFIdcShLbEHGZ1pmlvUeq3sr6YSdiSZ2LXNf3amr6efaukj iayjMjnsYlwNZiwMJosDd7xDMk1U8gKA8bwGP+WTy2wFBXeEpmRsi2Ivj7myP7FyyD m9mZZFJ0sA0qj0u0AQ7Jhc6QZIj/h2y7YWQ4ceKE= Received: from lingrow.int.hansenpartnership.com (unknown [IPv6:2601:5c4:4302:c21::a774]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange x25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lamorak.hansenpartnership.com (Postfix) with ESMTPSA id 60C4D1C015B; Wed, 02 Apr 2025 12:03:25 -0400 (EDT) Message-ID: <69225f4021ded9337a80cd926856ff3c05774427.camel@HansenPartnership.com> Subject: Re: [PATCH v2 2/4] fs: allow all writers to be frozen From: James Bottomley To: Christian Brauner , jack@suse.cz, peterz@infradead.org Cc: Ard Biesheuvel , linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, mcgrof@kernel.org, hch@infradead.org, david@fromorbit.com, rafael@kernel.org, djwong@kernel.org, pavel@kernel.org, mingo@redhat.com, will@kernel.org, boqun.feng@gmail.com, linux-fsdevel@vger.kernel.org Date: Wed, 02 Apr 2025 12:03:24 -0400 In-Reply-To: <20250402-melden-kindisch-8ea1b8c62bb4@brauner> References: <20250402-work-freeze-v2-0-6719a97b52ac@kernel.org> <20250402-work-freeze-v2-2-6719a97b52ac@kernel.org> <20250402-melden-kindisch-8ea1b8c62bb4@brauner> Autocrypt: addr=James.Bottomley@HansenPartnership.com; prefer-encrypt=mutual; keydata=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 8mT2Eh9SkH+YVOmaKsajgZgrBxA7fWmGoxXswEVxJIFj3vW7yNc0C5HaUdYa5iGOMs4kg2ht4s7yy7NRQuh7BifWjo6BQ6k4S1H+6axZucxhSV1L6zN9d+lr3Xo/vy1unzA== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.3 Precedence: bulk X-Mailing-List: linux-efi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2025-04-02 at 17:32 +0200, Christian Brauner wrote: [...] > Jan, one more thought about freezability here. We know that there > will can be at least one process during hibernation that ends up > generating page faults and that's systemd-journald. When systemd- > sleep requests writing a hibernation image via /sys/power/ files it > will inevitably end up freezing systemd-journald and it may be > generating a page fault with ->mmap_lock held. systemd-journald is > now sleeping with SB_FREEZE_PAGEFAULT and TASK_FREEZABLE. We know > this can cause hibernation to fail. That part is fine. What isn't is > that we will very likely always trigger: >=20 > #ifdef CONFIG_LOCKDEP > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * It's dangerous to free= ze with locks held; there be dragons > there. > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */ > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (!(state & __TASK_FREEZABLE= _UNSAFE)) > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0 WARN_ON_ONCE(debug_locks && p->lockdep_depth); > #endif >=20 > with lockdep enabled. >=20 > So we really actually need percpu_rswem_read_freezable_unsafe(), > i.e., TASK_FREEZABLE_UNSAFE. The sched people have pretty strong views about people not doing this, expressed in the comment in sched.h and commit f5d39b020809 ("freezer,sched: Rewrite core freezer logic") where most of the _unsafe variants got removed with prejudice. If we do get into this situation the worst that can happen is that another upper lock acquisition triggers a hibernate failure and we thaw everything, thus we can never truly deadlock, which is the fear, so perhaps they might be OK with this. Note that Rafael's solution to this was to disable lockdep around hibernate/suspend and resume, which is another possibility. Regards, James