From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 558241C5485 for ; Mon, 19 May 2025 12:30:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747657842; cv=none; b=PFvIcEXsZc/BvrAl/iVWd+Xrs0ESGpCIiW3aK9APdElNR7iaDGPUnPXSPT/lp8yXslgynamcl0Ur+4JO47dZftC+xvh+/+i1Cb5RE0YSqi1btjnVvKmfguz2f9ABnocyn5veDcWKQVdATPq8v1xo3p4vu/hpKQILg8TxBgniSvw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747657842; c=relaxed/simple; bh=uwH35vZskqnFQCg782XfN3Nzayyc+Vps7Iy4QAYu7XQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=TPSgwY1brqoD/9x9haU1rq98FHClMfbuniimOYliLeQBpDK/gZdm3uRFcBiz6XLiPknyzeQxoXRC82uPtnuEBu86mIqP3yC/rmWnMe6bT944ia26rE7BdlksMKG3ABa+YIv2CZ7JFLwRLvZ1trHT6ps9JHRVB6FGMzkzYCNvAgU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=CZr7MBTo; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="CZr7MBTo" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1747657839; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=9WKrghLuANfXdQygrmbp9TAaeInx1YgSzFxjYIUOcyQ=; b=CZr7MBToArOtdfbd7TFFb/Xqs0ovUUvhK7+0OieUQAhhlhreGZrdCVbp9Fdj1duz4JeMnL 3mqaEonoHL6SBMhqGuyVahGsfRAvFD355nz5fnn/X/Ps3JnEyZ6evBliQTo2QXH8E0Dvad mMO6IJWOsvDoYNJg33J55rSc0pyKh/U= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-551-4ABGkcQ3OHS2PrRRIrlTHw-1; Mon, 19 May 2025 08:30:35 -0400 X-MC-Unique: 4ABGkcQ3OHS2PrRRIrlTHw-1 X-Mimecast-MFC-AGG-ID: 4ABGkcQ3OHS2PrRRIrlTHw_1747657835 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (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 mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id D963C1956096; Mon, 19 May 2025 12:30:34 +0000 (UTC) Received: from bfoster (unknown [10.22.64.135]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 241EA195608D; Mon, 19 May 2025 12:30:33 +0000 (UTC) Date: Mon, 19 May 2025 08:34:01 -0400 From: Brian Foster To: Jan Kara Cc: linux-ext4@vger.kernel.org Subject: Re: [PATCH] ext4: only dirty folios when data journaling regular files Message-ID: References: <20250516173800.175577-1-bfoster@redhat.com> Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 On Mon, May 19, 2025 at 12:24:32PM +0200, Jan Kara wrote: > On Fri 16-05-25 13:38:00, Brian Foster wrote: > > fstest generic/388 occasionally reproduces a crash that looks as > > follows: > > > > BUG: kernel NULL pointer dereference, address: 0000000000000000 > > ... > > Call Trace: > > > > ext4_block_zero_page_range+0x30c/0x380 [ext4] > > ext4_truncate+0x436/0x440 [ext4] > > ext4_process_orphan+0x5d/0x110 [ext4] > > ext4_orphan_cleanup+0x124/0x4f0 [ext4] > > ext4_fill_super+0x262d/0x3110 [ext4] > > get_tree_bdev_flags+0x132/0x1d0 > > vfs_get_tree+0x26/0xd0 > > vfs_cmd_create+0x59/0xe0 > > __do_sys_fsconfig+0x4ed/0x6b0 > > do_syscall_64+0x82/0x170 > > ... > > > > This occurs when processing a symlink inode from the orphan list. The > > partial block zeroing code in the truncate path calls > > ext4_dirty_journalled_data() -> folio_mark_dirty(). The latter calls > > mapping->a_ops->dirty_folio(), but symlink inodes are not assigned an > > a_ops vector in ext4, hence the crash. > > > > To avoid this problem, update the ext4_dirty_journalled_data() helper to > > only mark the folio dirty on regular files (for which a_ops is > > assigned). This also matches the journaling logic in the ext4_symlink() > > creation path, where ext4_handle_dirty_metadata() is called directly. > > > > Fixes: d84c9ebdac1e ("ext4: Mark pages with journalled data dirty") > > Signed-off-by: Brian Foster > > Yeah, I forgot about this subtlety when writing d84c9ebdac1e. Good catch > and thanks for fixing this up! The fix looks good. Feel free to add: > > Reviewed-by: Jan Kara > > > --- > > > > Hi Jan, > > > > I'm not intimately familiar with the jbd machinery here so this may well > > be wrong, but it survives my testing so far. I initially hacked this to > > mark the buffer dirty instead of the folio, but discovered jbd2 doesn't > > seem to like that. I suspect that is because jbd2 wants to dirty/submit > > the buffer itself after it's logged..? > > > > Anyways, after that, this struck me as most consistent with behavior > > prior to d84c9ebdac1e and/or with the creation path, so I'm floating > > this as a first pass. Is my understanding of d84c9ebdac1e correct in > > that it is mainly an optimization to allow writeback to force the > > journaling mechanism vs. otherwise waiting for the other way around > > (i.e. a journal commit to mark folios dirty)? Thoughts appreciated.. > > Well, the motivation for d84c9ebdac1e was not so much an optimization but > rather to provide better visibility to the generic code what needs writing > out. Otherwise we had to special-case data journalling in a lot of places > that tried to do "clean the inode & purge the page cache" because simple > filemap_write_and_wait() was not enough to get the dirty pages in the inode > to disk. > Ah, I see. Thanks for the insight (and review). Brian > Honza > > > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c > > index 94c7d2d828a6..d3c138003ad3 100644 > > --- a/fs/ext4/inode.c > > +++ b/fs/ext4/inode.c > > @@ -1009,7 +1009,12 @@ int ext4_walk_page_buffers(handle_t *handle, struct inode *inode, > > */ > > static int ext4_dirty_journalled_data(handle_t *handle, struct buffer_head *bh) > > { > > - folio_mark_dirty(bh->b_folio); > > + struct folio *folio = bh->b_folio; > > + struct inode *inode = folio->mapping->host; > > + > > + /* only regular files have a_ops */ > > + if (S_ISREG(inode->i_mode)) > > + folio_mark_dirty(folio); > > return ext4_handle_dirty_metadata(handle, NULL, bh); > > } > > > > -- > > 2.49.0 > > > -- > Jan Kara > SUSE Labs, CR >