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From: Ross Zwisler <ross.zwisler@linux.intel.com>
To: rdodgen@gmail.com
Cc: linux-ext4@vger.kernel.org, tytso@mit.edu,
	Randy Dodgen <dodgen@google.com>,
	linux-nvdimm@lists.01.org
Subject: Re: [PATCH v3] Fix ext4 fault handling when mounted with -o dax,ro
Date: Thu, 24 Aug 2017 09:11:38 -0600	[thread overview]
Message-ID: <20170824151138.GA25588@linux.intel.com> (raw)
In-Reply-To: <416a465a9fbe1d27085883dbf652c115cd195697.1503523424.git.dodgen@google.com>

On Wed, Aug 23, 2017 at 02:26:52PM -0700, rdodgen@gmail.com wrote:
> From: Randy Dodgen <dodgen@google.com>
> 
> If an ext4 filesystem is mounted with both the DAX and read-only
> options, executables on that filesystem will fail to start (claiming
> 'Segmentation fault') due to the fault handler returning
> VM_FAULT_SIGBUS.
> 
> This is due to the DAX fault handler (see ext4_dax_huge_fault)
> attempting to write to the journal when FAULT_FLAG_WRITE is set. This is
> the wrong behavior for write faults which will lead to a COW page; in
> particular, this fails for readonly mounts.
> 
> This change avoids journal writes for faults that are expected to COW.
> 
> It might be the case that this could be better handled in
> ext4_iomap_begin / ext4_iomap_end (called via iomap_ops inside
> dax_iomap_fault). These is some overlap already (e.g. grabbing journal
> handles).
> 
> Signed-off-by: Randy Dodgen <dodgen@google.com>

Cool, looks good from the DAX point of view.  You can add:

Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
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WARNING: multiple messages have this Message-ID (diff)
From: Ross Zwisler <ross.zwisler-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
To: rdodgen-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
Cc: linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	tytso-3s7WtUTddSA@public.gmane.org,
	Randy Dodgen <dodgen-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
	linux-nvdimm-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org
Subject: Re: [PATCH v3] Fix ext4 fault handling when mounted with -o dax,ro
Date: Thu, 24 Aug 2017 09:11:38 -0600	[thread overview]
Message-ID: <20170824151138.GA25588@linux.intel.com> (raw)
In-Reply-To: <416a465a9fbe1d27085883dbf652c115cd195697.1503523424.git.dodgen-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>

On Wed, Aug 23, 2017 at 02:26:52PM -0700, rdodgen-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org wrote:
> From: Randy Dodgen <dodgen-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> 
> If an ext4 filesystem is mounted with both the DAX and read-only
> options, executables on that filesystem will fail to start (claiming
> 'Segmentation fault') due to the fault handler returning
> VM_FAULT_SIGBUS.
> 
> This is due to the DAX fault handler (see ext4_dax_huge_fault)
> attempting to write to the journal when FAULT_FLAG_WRITE is set. This is
> the wrong behavior for write faults which will lead to a COW page; in
> particular, this fails for readonly mounts.
> 
> This change avoids journal writes for faults that are expected to COW.
> 
> It might be the case that this could be better handled in
> ext4_iomap_begin / ext4_iomap_end (called via iomap_ops inside
> dax_iomap_fault). These is some overlap already (e.g. grabbing journal
> handles).
> 
> Signed-off-by: Randy Dodgen <dodgen-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>

Cool, looks good from the DAX point of view.  You can add:

Reviewed-by: Ross Zwisler <ross.zwisler-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>

  parent reply	other threads:[~2017-08-24 15:09 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-22 22:24 [PATCH] Fix ext4 fault handling when mounted with -o dax,ro Randy Dodgen
2017-08-23  3:37 ` [PATCH v2] " rdodgen
2017-08-23  3:37   ` rdodgen
2017-08-23 16:38   ` Ross Zwisler
2017-08-23 16:38     ` Ross Zwisler
2017-08-23 20:11     ` Randy Dodgen
2017-08-23 20:11       ` Randy Dodgen
2017-08-23 21:26       ` [PATCH v3] " rdodgen
2017-08-23 21:26         ` rdodgen
2017-08-24 14:45         ` Jan Kara
2017-08-24 14:45           ` Jan Kara
2017-08-24 15:11         ` Ross Zwisler [this message]
2017-08-24 15:11           ` Ross Zwisler
2017-08-24 16:01         ` Christoph Hellwig
2017-08-24 16:01           ` Christoph Hellwig
2017-08-24 20:57           ` Theodore Ts'o
2017-08-24 20:57             ` Theodore Ts'o
2017-08-25  7:28             ` Christoph Hellwig
2017-08-25  7:28               ` Christoph Hellwig
2017-08-29 21:20           ` Christoph Hellwig
2017-08-29 21:20             ` Christoph Hellwig
2017-08-29 21:37             ` Ross Zwisler
2017-08-29 21:37               ` Ross Zwisler
2017-08-29 22:07               ` Randy Dodgen
2017-08-29 22:07                 ` Randy Dodgen
2017-08-29 22:37               ` [fstests PATCH] generic: add test for executables on read-only DAX mounts Ross Zwisler
2017-08-29 22:37                 ` Ross Zwisler
2017-08-30 10:59                 ` Eryu Guan
2017-08-30 10:59                   ` Eryu Guan
2017-08-31  4:01                   ` Ross Zwisler
2017-08-31  4:01                     ` Ross Zwisler
2017-08-31  4:01                     ` Ross Zwisler
2017-08-31  4:09                   ` [fstests v2] " Ross Zwisler
2017-08-31  4:09                     ` Ross Zwisler
2017-08-30 14:51                 ` [fstests PATCH] " Christoph Hellwig
2017-08-30 14:51                   ` Christoph Hellwig
2017-08-30 14:51                   ` Christoph Hellwig
2017-08-31  4:02                   ` Ross Zwisler
2017-08-31  4:02                     ` Ross Zwisler
2017-08-31  4:02                     ` Ross Zwisler
2017-08-31 13:09                     ` Christoph Hellwig
2017-08-31 13:09                       ` Christoph Hellwig
2017-08-24 19:26         ` [PATCH v3] Fix ext4 fault handling when mounted with -o dax,ro Theodore Ts'o
2017-08-24 19:26           ` Theodore Ts'o

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