From: "Theodore Y. Ts'o" <tytso@mit.edu>
To: Jan Kara <jack@suse.cz>
Cc: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org,
Ross Zwisler <ross.zwisler@linux.intel.com>,
Dan Williams <dan.j.williams@intel.com>,
linux-mm@kvack.org, Dave Jiang <dave.jiang@intel.com>
Subject: Re: [PATCH] mm: Fix warning in insert_pfn()
Date: Wed, 3 Oct 2018 12:35:58 -0400 [thread overview]
Message-ID: <20181003163557.GA18434@thunk.org> (raw)
In-Reply-To: <20180824154542.26872-1-jack@suse.cz>
On Fri, Aug 24, 2018 at 05:45:42PM +0200, Jan Kara wrote:
> In DAX mode a write pagefault can race with write(2) in the following
> way:
>
> CPU0 CPU1
> write fault for mapped zero page (hole)
> dax_iomap_rw()
> iomap_apply()
> xfs_file_iomap_begin()
> - allocates blocks
> dax_iomap_actor()
> invalidate_inode_pages2_range()
> - invalidates radix tree entries in given range
> dax_iomap_pte_fault()
> grab_mapping_entry()
> - no entry found, creates empty
> ...
> xfs_file_iomap_begin()
> - finds already allocated block
> ...
> vmf_insert_mixed_mkwrite()
> - WARNs and does nothing because there
> is still zero page mapped in PTE
> unmap_mapping_pages()
>
> This race results in WARN_ON from insert_pfn() and is occasionally
> triggered by fstest generic/344. Note that the race is otherwise
> harmless as before write(2) on CPU0 is finished, we will invalidate page
> tables properly and thus user of mmap will see modified data from
> write(2) from that point on. So just restrict the warning only to the
> case when the PFN in PTE is not zero page.
>
> Signed-off-by: Jan Kara <jack@suse.cz>
I don't see this in linux-next. What's the status of this patch?
Thanks,
- Ted
next prev parent reply other threads:[~2018-10-03 16:35 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-24 15:45 [PATCH] mm: Fix warning in insert_pfn() Jan Kara
2018-10-03 16:35 ` Theodore Y. Ts'o [this message]
2018-10-03 16:56 ` Dan Williams
2018-10-04 14:35 ` Theodore Y. Ts'o
2018-10-11 0:30 ` Andrew Morton
2018-10-11 0:46 ` Dan Williams
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