From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3C281C77B60 for ; Fri, 28 Apr 2023 04:30:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345286AbjD1EaM (ORCPT ); Fri, 28 Apr 2023 00:30:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39468 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345179AbjD1EaL (ORCPT ); Fri, 28 Apr 2023 00:30:11 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D109630F7 for ; Thu, 27 Apr 2023 21:30:09 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 632F160E94 for ; Fri, 28 Apr 2023 04:30:09 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BF421C433EF; Fri, 28 Apr 2023 04:30:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1682656208; bh=/DghPxgc47hCMtL0NQGOIZbh9oxlkWYX91gG/1NLXFs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=J/4pGkinLKKzgj2T1gX2U6wS+840EHdmT3CwNuvSDxr4inCSp6eJ9Eg2XtMLg0xfl uBwJEE1cfD4rJA0Kl4G4MljqkMRQ5CvGPFUEfjNc9rUzNtMDrxwZQNP8gEPuuJ/eF2 gDC+BsNKDH3D3ciHuixauzmZ13kFECWS2qSSzbrnP5qa9A3eRzxB2F6/htvGxDoJzm eWxCIKl9ZMFv70WeFoH4UTvb+y9xRVmNnD8juqUgVpAbyyhinFq0ZjPzjiNVXOWrGr cWQw41PyPnMy3LlQhKC7vhcSvErmssEiFuPcpVtWNpYFf3szrjTA27rgNb/6NARcvB 9He/GgzD/tOog== Date: Thu, 27 Apr 2023 21:30:08 -0700 From: "Darrick J. Wong" To: Dave Chinner Cc: linux-xfs@vger.kernel.org Subject: Re: [PATCH 1/4] xfs: don't unconditionally null args->pag in xfs_bmap_btalloc_at_eof Message-ID: <20230428043008.GK59213@frogsfrogsfrogs> References: <168263573426.1717721.15565213947185049577.stgit@frogsfrogsfrogs> <168263573987.1717721.305790819127740342.stgit@frogsfrogsfrogs> <20230428014928.GN3223426@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230428014928.GN3223426@dread.disaster.area> Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Fri, Apr 28, 2023 at 11:49:28AM +1000, Dave Chinner wrote: > On Thu, Apr 27, 2023 at 03:48:59PM -0700, Darrick J. Wong wrote: > > From: Darrick J. Wong > > > > xfs/170 on a filesystem with su=128k,sw=4 produces this splat: > > > > BUG: kernel NULL pointer dereference, address: 0000000000000010 > > #PF: supervisor write access in kernel mode > > #PF: error_code(0x0002) - not-present page > > PGD 0 P4D 0 > > Oops: 0002 [#1] PREEMPT SMP > > CPU: 1 PID: 4022907 Comm: dd Tainted: G W 6.3.0-xfsx #2 6ebeeffbe9577d32 > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20171121_152543-x86-ol7-bu > > RIP: 0010:xfs_perag_rele+0x10/0x70 [xfs] > > RSP: 0018:ffffc90001e43858 EFLAGS: 00010217 > > RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000100 > > RDX: ffffffffa054e717 RSI: 0000000000000005 RDI: 0000000000000000 > > RBP: ffff888194eea000 R08: 0000000000000000 R09: 0000000000000037 > > R10: ffff888100ac1cb0 R11: 0000000000000018 R12: 0000000000000000 > > R13: ffffc90001e43a38 R14: ffff888194eea000 R15: ffff888194eea000 > > FS: 00007f93d1a0e740(0000) GS:ffff88843fc80000(0000) knlGS:0000000000000000 > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > CR2: 0000000000000010 CR3: 000000018a34f000 CR4: 00000000003506e0 > > Call Trace: > > > > xfs_bmap_btalloc+0x1a7/0x5d0 [xfs f85291d6841cbb3dc740083f1f331c0327394518] > > xfs_bmapi_allocate+0xee/0x470 [xfs f85291d6841cbb3dc740083f1f331c0327394518] > > xfs_bmapi_write+0x539/0x9e0 [xfs f85291d6841cbb3dc740083f1f331c0327394518] > > xfs_iomap_write_direct+0x1bb/0x2b0 [xfs f85291d6841cbb3dc740083f1f331c0327394518] > > xfs_direct_write_iomap_begin+0x51c/0x710 [xfs f85291d6841cbb3dc740083f1f331c0327394518] > > iomap_iter+0x132/0x2f0 > > __iomap_dio_rw+0x2f8/0x840 > > iomap_dio_rw+0xe/0x30 > > xfs_file_dio_write_aligned+0xad/0x180 [xfs f85291d6841cbb3dc740083f1f331c0327394518] > > xfs_file_write_iter+0xfb/0x190 [xfs f85291d6841cbb3dc740083f1f331c0327394518] > > vfs_write+0x2eb/0x410 > > ksys_write+0x65/0xe0 > > do_syscall_64+0x2b/0x80 > > > > This crash occurs under the "out_low_space" label. We grabbed a perag > > reference, passed it via args->pag into xfs_bmap_btalloc_at_eof, and > > afterwards args->pag is NULL. Fix the second function not to clobber > > args->pag if the caller had passed one in. > > > > Fixes: 85843327094f ("xfs: factor xfs_bmap_btalloc()") > > Signed-off-by: Darrick J. Wong > > --- > > fs/xfs/libxfs/xfs_bmap.c | 5 +++-- > > 1 file changed, 3 insertions(+), 2 deletions(-) > > > > > > diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c > > index b512de0540d5..cd8870a16fd1 100644 > > --- a/fs/xfs/libxfs/xfs_bmap.c > > +++ b/fs/xfs/libxfs/xfs_bmap.c > > @@ -3494,8 +3494,10 @@ xfs_bmap_btalloc_at_eof( > > if (!caller_pag) > > args->pag = xfs_perag_get(mp, XFS_FSB_TO_AGNO(mp, ap->blkno)); > > error = xfs_alloc_vextent_exact_bno(args, ap->blkno); > > - if (!caller_pag) > > + if (!caller_pag) { > > xfs_perag_put(args->pag); > > + args->pag = NULL; > > + } > > if (error) > > return error; > > > > @@ -3505,7 +3507,6 @@ xfs_bmap_btalloc_at_eof( > > * Exact allocation failed. Reset to try an aligned allocation > > * according to the original allocation specification. > > */ > > - args->pag = NULL; > > args->alignment = stripe_align; > > args->minlen = nextminlen; > > args->minalignslop = 0; > > Yup, that'll fix the problem. > > Reviewed-by: Dave Chinner > > FWIW, I'm working on some patches to take this further by always > providing a caller perag to this function. That gets rid of all the > conditional code here and it gets rid of the only case where we call > xfs_alloc_vextent_near_bno() without args->pag set so the > conditional caller_pag code goes from there, too. This makes > xfs_alloc_vextent_{near,exact}_bno() identical except for one line > so they can be collapsed. And now that we always specify args->pag > for these functions, we can ignore the agno part of the target block > meaning we can select the perag to allocate from at a much higher > level via setting up args->pag when we initially scan the AGs to > set up args->minlen/maxlen based on the the nearest AG with > contiguous free space large enough for the whole allocation. This > avoids attempting allocations that are guaranteed to fail before > we fall back to iterating from the target block agno and eventually > finding the same AG we originally found that had enough contiguous > free space in it for a maxlen allocation.... > > I think I can take it further an make both filestreams and the > normal allocator use the same "this ag" algorithm for EOF and > aligned allocation and then have them both fall back to the same > unaligned allocation attempts, which will then allow a bunch of code > to be collapsed in the xfs_bmap_btalloc() path... I was thinking along those lines too when I was writing this patch, but for now I'll just patch everything back together. :) That /would/ make the interfaces to those functions a lot more consistent. --D > -Dave. > -- > Dave Chinner > david@fromorbit.com