From: Dan Williams <dan.j.williams@intel.com>
To: Ross Zwisler <ross.zwisler@linux.intel.com>,
Christoph Hellwig <hch@infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Dan Williams <dan.j.williams@intel.com>,
Dave Chinner <david@fromorbit.com>, Jan Kara <jack@suse.com>,
Matthew Wilcox <willy@linux.intel.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-nvdimm <linux-nvdimm@ml01.01.org>
Subject: Re: [PATCH 2/2] dax: fix bdev NULL pointer dereferences
Date: Fri, 29 Jan 2016 16:18:22 -0800 [thread overview]
Message-ID: <CAPcyv4iwZjmLxtEZWcExB5hCH765NVeNgiiYzKbeefGYDMBHWQ@mail.gmail.com> (raw)
In-Reply-To: <20160129233430.GA20549@linux.intel.com>
On Fri, Jan 29, 2016 at 3:34 PM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> On Fri, Jan 29, 2016 at 11:28:15AM -0700, Ross Zwisler wrote:
>> On Thu, Jan 28, 2016 at 01:38:58PM -0800, Christoph Hellwig wrote:
>> > On Thu, Jan 28, 2016 at 12:35:04PM -0700, Ross Zwisler wrote:
>> > > There are a number of places in dax.c that look up the struct block_device
>> > > associated with an inode. Previously this was done by just using
>> > > inode->i_sb->s_bdev. This is correct for inodes that exist within the
>> > > filesystems supported by DAX (ext2, ext4 & XFS), but when running DAX
>> > > against raw block devices this value is NULL. This causes NULL pointer
>> > > dereferences when these block_device pointers are used.
>> >
>> > It's also wrong for an XFS file system with a RT device..
>> >
>> > > +#define DAX_BDEV(inode) (S_ISBLK(inode->i_mode) ? I_BDEV(inode) \
>> > > + : inode->i_sb->s_bdev)
>> >
>> > .. but this isn't going to fix it. You must use a bdev returned by
>> > get_blocks or a similar file system method.
>>
>> I guess I need to go off and understand if we can have DAX mappings on such a
>> device. If we can, we may have a problem - we can get the block_device from
>> get_block() in I/O path and the various fault paths, but we don't have access
>> to get_block() when flushing via dax_writeback_mapping_range(). We avoid
>> needing it the normal case by storing the sector results from get_block() in
>> the radix tree.
>>
>> /me is off to play with RT devices...
>
> Well, RT devices are completely broken as far as I can see. I've reported the
> breakage to the XFS list. Anything I do that triggers a RT block allocation
> in XFS causes a lockdep splat + a kernel BUG - I've tried regular pwrite(),
> xfs_rtcp and mmap() + write to address. Not a new bug either - happens just
> the same with v4.4. Happens with both PMEM and BRD, and has no relationship
> to whether I'm using DAX or not.
>
> Does it work for this patch to go in as-is since it fixes an immediate OOPS
> with raw block devices + DAX, and when RT devices are alive again I'll figure
> out how to make them work too?
Can we step back and be clear about which lookups should be coming
from get_blocks(). Which ones are critical vs ones we just
opportunistically lookup for a debug print.
Right now xfs and ext4 are basically disagreeing on whether
get_blocks() reliably sets ->bh_bdev, and checking for a raw
block-device inode in dax_clear_blocks() does not make sense. So this
all seems a bit confused.
next prev parent reply other threads:[~2016-01-30 0:18 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-28 19:35 [PATCH 1/2] block: fix pfn_mkwrite() DAX fault handler Ross Zwisler
2016-01-28 19:35 ` [PATCH 2/2] dax: fix bdev NULL pointer dereferences Ross Zwisler
2016-01-28 20:21 ` Dan Williams
2016-01-28 21:38 ` Christoph Hellwig
2016-01-29 18:28 ` Ross Zwisler
2016-01-29 23:34 ` Ross Zwisler
2016-01-30 0:18 ` Dan Williams [this message]
2016-01-31 22:44 ` Dave Chinner
2016-01-30 5:28 ` Matthew Wilcox
2016-01-30 6:01 ` Dan Williams
2016-01-30 7:08 ` Jared Hulbert
2016-01-31 2:32 ` Matthew Wilcox
2016-01-31 6:12 ` Ross Zwisler
2016-01-31 10:55 ` Matthew Wilcox
2016-01-31 16:38 ` Dan Williams
2016-01-31 18:07 ` Matthew Wilcox
2016-01-31 18:18 ` Dan Williams
2016-01-31 18:27 ` Matthew Wilcox
2016-01-31 18:50 ` Dan Williams
2016-01-31 19:51 ` Dan Williams
2016-02-01 13:44 ` Matthew Wilcox
2016-02-01 14:51 ` Jan Kara
2016-02-01 20:49 ` Matthew Wilcox
2016-02-01 21:47 ` Dave Chinner
2016-02-02 6:06 ` Jared Hulbert
2016-02-02 6:46 ` Dan Williams
2016-02-02 8:05 ` Jared Hulbert
2016-02-02 16:51 ` Dan Williams
2016-02-02 21:46 ` Jared Hulbert
2016-02-03 0:34 ` Matthew Wilcox
2016-02-03 1:21 ` Jared Hulbert
2016-02-02 11:17 ` Jan Kara
2016-02-02 16:33 ` Dan Williams
2016-02-02 16:46 ` Jan Kara
2016-02-02 17:10 ` Dan Williams
2016-02-02 17:34 ` Ross Zwisler
2016-02-02 17:46 ` Dan Williams
2016-02-02 17:47 ` Dan Williams
2016-02-02 18:24 ` Ross Zwisler
2016-02-02 18:46 ` Matthew Wilcox
2016-02-02 18:59 ` Dan Williams
2016-02-02 20:14 ` Matthew Wilcox
2016-02-03 11:09 ` Jan Kara
2016-02-03 10:46 ` Jan Kara
2016-02-03 20:13 ` Ross Zwisler
2016-02-04 9:15 ` Jan Kara
2016-02-04 23:38 ` Ross Zwisler
2016-02-06 23:15 ` Dave Chinner
2016-02-07 5:27 ` Ross Zwisler
2016-02-04 19:56 ` Ross Zwisler
2016-02-04 20:29 ` Jan Kara
2016-02-04 22:19 ` Ross Zwisler
2016-02-05 22:25 ` Ross Zwisler
2016-02-06 23:40 ` Dave Chinner
2016-02-07 6:43 ` Ross Zwisler
2016-02-08 13:48 ` Jan Kara
2016-02-07 8:38 ` Christoph Hellwig
2016-02-08 15:55 ` Ross Zwisler
2016-02-02 18:41 ` Ross Zwisler
2016-02-02 18:53 ` Ross Zwisler
2016-02-02 0:02 ` Ross Zwisler
2016-02-02 7:10 ` Dave Chinner
2016-02-02 10:34 ` Jan Kara
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