linux-kernel - Re: [PATCH v5 03/25] fs/dax: Don't skip locked entries when scanning entries

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <677f013c1466_f58f29466@dwillia2-xfh.jf.intel.com.notmuch>
Date: Wed, 8 Jan 2025 14:50:36 -0800
From: Dan Williams <dan.j.williams@...el.com>
To: Alistair Popple <apopple@...dia.com>, <akpm@...ux-foundation.org>,
	<dan.j.williams@...el.com>, <linux-mm@...ck.org>
CC: Alistair Popple <apopple@...dia.com>, <lina@...hilina.net>,
	<zhang.lyra@...il.com>, <gerald.schaefer@...ux.ibm.com>,
	<vishal.l.verma@...el.com>, <dave.jiang@...el.com>, <logang@...tatee.com>,
	<bhelgaas@...gle.com>, <jack@...e.cz>, <jgg@...pe.ca>,
	<catalin.marinas@....com>, <will@...nel.org>, <mpe@...erman.id.au>,
	<npiggin@...il.com>, <dave.hansen@...ux.intel.com>, <ira.weiny@...el.com>,
	<willy@...radead.org>, <djwong@...nel.org>, <tytso@....edu>,
	<linmiaohe@...wei.com>, <david@...hat.com>, <peterx@...hat.com>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linuxppc-dev@...ts.ozlabs.org>,
	<nvdimm@...ts.linux.dev>, <linux-cxl@...r.kernel.org>,
	<linux-fsdevel@...r.kernel.org>, <linux-ext4@...r.kernel.org>,
	<linux-xfs@...r.kernel.org>, <jhubbard@...dia.com>, <hch@....de>,
	<david@...morbit.com>
Subject: Re: [PATCH v5 03/25] fs/dax: Don't skip locked entries when scanning
 entries

Alistair Popple wrote:
> Several functions internal to FS DAX use the following pattern when
> trying to obtain an unlocked entry:
> 
>     xas_for_each(&xas, entry, end_idx) {
> 	if (dax_is_locked(entry))
> 	    entry = get_unlocked_entry(&xas, 0);
> 
> This is problematic because get_unlocked_entry() will get the next
> present entry in the range, and the next entry may not be
> locked. Therefore any processing of the original locked entry will be
> skipped. This can cause dax_layout_busy_page_range() to miss DMA-busy
> pages in the range, leading file systems to free blocks whilst DMA
> operations are ongoing which can lead to file system corruption.
> 
> Instead callers from within a xas_for_each() loop should be waiting
> for the current entry to be unlocked without advancing the XArray
> state so a new function is introduced to wait.

Oh wow, good eye!

Did this trip up an xfstest, or did you see this purely by inspection?

> Also while we are here rename get_unlocked_entry() to
> get_next_unlocked_entry() to make it clear that it may advance the
> iterator state.

Outside of the above clarification of how found / end user effect you
can add:

Reviewed-by: Dan Williams <dan.j.williams@...el.com>