From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 0D05D43147; Tue, 9 Jul 2024 15:27:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720538862; cv=none; b=CgWvAqKRK3YVpK+m2fgvEsLqGO2Ra3aDbdygqnMN7FritRqybB6xjJZ8wWt07uOb/ewFkDrHBgYFNbuwndt6AyeAxpl8Obr6FdE7rv9dr/eCjdasUOOS49vharyiBk3mGohMWdhZl4S6CYAOycR0ip2ENImV5Py5fXP6goCRFto= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720538862; c=relaxed/simple; bh=O0o3i35g9yIYq7V1d5PS5NTZJHLF+8SpUYDRPKu7OO4=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=U4bJLZROZPdG88+8/ed3ps6DaQZGy33qZVt0ZwqR1hrY4xPjvg8XC/G7MEn/UdrzVKsXYBRSph83JENm67YYvFidHjw1PEB3TCoSqrcZpJHuyp8f6K2EqOSk798NIdf8AJmX8ofi+YmNYbISPJrhEQ60vq8DlucMWTqLN+0LmbI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=C4Ywpoy6; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="C4Ywpoy6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5E471C32782; Tue, 9 Jul 2024 15:27:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1720538861; bh=O0o3i35g9yIYq7V1d5PS5NTZJHLF+8SpUYDRPKu7OO4=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=C4Ywpoy6K5wIoIRwcQNFUBcFBSm+8LwYLbaOFn62U9hkqPOC3Xnp3SAClvusoEu/4 t8PRG95A7Jh+FvPMm+Wsh/PIwjOyavjD16xowvdOXr+ZkLNrEHc7NywXAwTlaW2/84 L5fDlxJ52lV97hEa9XAM4Z0Qn2BpkbqwHaFsng0dM/I4u1TZonELVmo2XR8U+U0B3a OOT8Bs6m8EwF+G50dpIP0OET5Njsa9AL7rC7aYIW9MFRSdAuCsBQbhydmmhr0V3nGn 4lY3OsaqdOEJr7kMH/5OHPjt68AtrtYmRHdbQBGPxGYhV1KMQgfd1sqBPlQuuLkj/A qg+N0VUr5wxWQ== Message-ID: Subject: Re: [jlayton:mgtime 5/13] inode.c:undefined reference to `__invalid_cmpxchg_size' From: Jeff Layton To: Arnd Bergmann , Geert Uytterhoeven Cc: linux-m68k@lists.linux-m68k.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Date: Tue, 09 Jul 2024 11:27:40 -0400 In-Reply-To: <92726965-19a0-433b-9b49-69af84b25081@app.fastmail.com> References: <202407091931.mztaeJHw-lkp@intel.com> <6ab599393503a50b4b708767f320a46388aa95f2.camel@kernel.org> <92726965-19a0-433b-9b49-69af84b25081@app.fastmail.com> Autocrypt: addr=jlayton@kernel.org; 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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.4 (3.50.4-1.fc39) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2024-07-09 at 17:07 +0200, Arnd Bergmann wrote: > On Tue, Jul 9, 2024, at 16:23, Jeff Layton wrote: > > On Tue, 2024-07-09 at 16:16 +0200, Arnd Bergmann wrote: > > > On Tue, Jul 9, 2024, at 15:45, Geert Uytterhoeven wrote: > >=20 > > I think the simplest solution is to make the floor value I'm > > tracking > > be an atomic64_t. That looks like it should smooth over the > > differences > > between arches. I'm testing a patch to do that now. >=20 > Yes, atomic64_t should work, but be careful about using this > in a fast path since it can turn into a global spinlock > in lib/atomic64.c on architectures that don't support it > natively. >=20 > I'm still reading through the rest of your series, but > it appears that you pass the time value into=20 > ktime_to_timespec64() directly afterwards, so I guess > that is already a fairly large overhead on 32-bit > architectures and an extra spinlock doesn't hurt too > much. >=20 Thanks Arnd. The context for this is generally a write or other change to an inode, so I too am hoping the overhead won't be too bad. It does take great pains to avoid changing the ctime_floor value whenever possible. > Two more things I noticed in your patch: >=20 > - smp_load_acquire() on a 64-bit variable seems problematic > =C2=A0 as well, maybe this needs a spinlock on 32-bit > =C2=A0 architectures? >=20 That should go away with the conversion of ctime_floor to atomic64_t. AFAICT, arches that don't have native a 64-bit cmpxchg op usually emulate that with hashed spinlocks.=20 > - for the coarse_ctime function, I think you should be > =C2=A0 able to avoid the conversion to timespec by just calling > =C2=A0 ktime_get_coarse_real_ts64() again instead of converting > =C2=A0 monotonic to real and then to timespec. >=20 Note that we might get different values for the coarse timestamps, but if we do then the second fetch will just be a little later (which is OK). I'll plan to make this change. > - inode_set_ctime_current() seems to now store a fine-grained > =C2=A0 timespec in the inode even for the !is_mgtime case, skipping > =C2=A0 the timestamp_truncate() step. This appears to potentially > =C2=A0 leak a non-truncated value to userspace, which would be > =C2=A0 inconsistent with the value read back from disk. Oof, you're right. I'll fix that up for the next version. Thanks for the review! --=20 Jeff Layton