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[RFC] [PATCH] xen/blkback: add locking in statistics sysfs show functions

 

 

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msw at amazon

Apr 20, 2012, 12:21 PM

Post #1 of 4 (162 views)
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[RFC] [PATCH] xen/blkback: add locking in statistics sysfs show functions

This is a port of a patch in the XenoLinux 2.6.18 tree:
http://xenbits.xen.org/hg/linux-2.6.18-xen.hg/rev/f47c07325a56

Fix blkback sysfs race

Read blkback statistics info after remove vbd device(s) kernel
will crash.

Signed-off-by: Joe Jin <joe.jin [at] oracle>
Acked-by: Jan Beulich <jbeulich [at] novell>
[Ported to Linux 3.x]
Signed-off-by: Matt Wilson <msw [at] amazon>
---
drivers/block/xen-blkback/xenbus.c | 20 +++++++++++++++++---
1 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index da19506..74d4810 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -21,6 +21,8 @@
#include <xen/grant_table.h>
#include "common.h"

+static DEFINE_RWLOCK(sysfs_read_lock);
+
struct backend_info {
struct xenbus_device *dev;
struct xen_blkif *blkif;
@@ -225,10 +227,20 @@ int __init xen_blkif_interface_init(void)
struct device_attribute *attr, \
char *buf) \
{ \
- struct xenbus_device *dev = to_xenbus_device(_dev); \
- struct backend_info *be = dev_get_drvdata(&dev->dev); \
+ ssize_t ret = -ENODEV; \
+ struct xenbus_device *dev; \
+ struct backend_info *be; \
\
- return sprintf(buf, format, ##args); \
+ if (!get_device(_dev)) \
+ return ret; \
+ dev = to_xenbus_device(_dev); \
+ read_lock(&sysfs_read_lock); \
+ be = (struct backend_info *) dev_get_drvdata(&dev->dev);\
+ if (be != NULL) \
+ ret = sprintf(buf, format, ##args); \
+ read_unlock(&sysfs_read_lock); \
+ put_device(_dev); \
+ return ret; \
} \
static DEVICE_ATTR(name, S_IRUGO, show_##name, NULL)

@@ -353,6 +365,7 @@ static int xen_blkbk_remove(struct xenbus_device *dev)

DPRINTK("");

+ write_lock(&sysfs_read_lock);
if (be->major || be->minor)
xenvbd_sysfs_delif(dev);

@@ -371,6 +384,7 @@ static int xen_blkbk_remove(struct xenbus_device *dev)

kfree(be);
dev_set_drvdata(&dev->dev, NULL);
+ write_unlock(&sysfs_read_lock);
return 0;
}

--
1.7.2.5


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konrad.wilk at oracle

Apr 26, 2012, 1:51 PM

Post #2 of 4 (142 views)
Permalink
Re: [RFC] [PATCH] xen/blkback: add locking in statistics sysfs show functions [In reply to]

On Fri, Apr 20, 2012 at 07:21:13PM +0000, Matt Wilson wrote:
> This is a port of a patch in the XenoLinux 2.6.18 tree:
> http://xenbits.xen.org/hg/linux-2.6.18-xen.hg/rev/f47c07325a56
>
> Fix blkback sysfs race
>
> Read blkback statistics info after remove vbd device(s) kernel
> will crash.

Looks pretty reasonable.

>
> Signed-off-by: Joe Jin <joe.jin [at] oracle>
> Acked-by: Jan Beulich <jbeulich [at] novell>
> [Ported to Linux 3.x]
> Signed-off-by: Matt Wilson <msw [at] amazon>
> ---
> drivers/block/xen-blkback/xenbus.c | 20 +++++++++++++++++---
> 1 files changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
> index da19506..74d4810 100644
> --- a/drivers/block/xen-blkback/xenbus.c
> +++ b/drivers/block/xen-blkback/xenbus.c
> @@ -21,6 +21,8 @@
> #include <xen/grant_table.h>
> #include "common.h"
>
> +static DEFINE_RWLOCK(sysfs_read_lock);
> +
> struct backend_info {
> struct xenbus_device *dev;
> struct xen_blkif *blkif;
> @@ -225,10 +227,20 @@ int __init xen_blkif_interface_init(void)
> struct device_attribute *attr, \
> char *buf) \
> { \
> - struct xenbus_device *dev = to_xenbus_device(_dev); \
> - struct backend_info *be = dev_get_drvdata(&dev->dev); \
> + ssize_t ret = -ENODEV; \
> + struct xenbus_device *dev; \
> + struct backend_info *be; \
> \
> - return sprintf(buf, format, ##args); \
> + if (!get_device(_dev)) \
> + return ret; \
> + dev = to_xenbus_device(_dev); \
> + read_lock(&sysfs_read_lock); \
> + be = (struct backend_info *) dev_get_drvdata(&dev->dev);\
> + if (be != NULL) \
> + ret = sprintf(buf, format, ##args); \
> + read_unlock(&sysfs_read_lock); \
> + put_device(_dev); \
> + return ret; \
> } \
> static DEVICE_ATTR(name, S_IRUGO, show_##name, NULL)
>
> @@ -353,6 +365,7 @@ static int xen_blkbk_remove(struct xenbus_device *dev)
>
> DPRINTK("");
>
> + write_lock(&sysfs_read_lock);
> if (be->major || be->minor)
> xenvbd_sysfs_delif(dev);
>
> @@ -371,6 +384,7 @@ static int xen_blkbk_remove(struct xenbus_device *dev)
>
> kfree(be);
> dev_set_drvdata(&dev->dev, NULL);
> + write_unlock(&sysfs_read_lock);
> return 0;
> }
>
> --
> 1.7.2.5

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konrad.wilk at oracle

Apr 26, 2012, 7:24 PM

Post #3 of 4 (141 views)
Permalink
Re: [RFC] [PATCH] xen/blkback: add locking in statistics sysfs show functions [In reply to]

On Fri, Apr 20, 2012 at 07:21:13PM +0000, Matt Wilson wrote:
> This is a port of a patch in the XenoLinux 2.6.18 tree:
> http://xenbits.xen.org/hg/linux-2.6.18-xen.hg/rev/f47c07325a56
>
> Fix blkback sysfs race

So with this patch I keep on getting this:

[ 128.274290] switch: port 2(vif1.0) entered disabled state
[ 128.855442] BUG: sleeping function called from invalid context at /home/konrad/ssd/linux/kernel/mutex.c:85
[ 128.855628] in_atomic(): 1, irqs_disabled(): 0, pid: 46, name: xenwatch
[ 128.855757] Pid: 46, comm: xenwatch Tainted: G O 3.4.0-rc4upstream-00103-g7e4325c-dirty #1
[ 128.855917] Call Trace:
[ 128.856062] [<ffffffff810983ea>] __might_sleep+0xda/0x100
[ 128.856215] [<ffffffff815a9267>] mutex_lock+0x27/0x50
[ 128.856351] [<ffffffff811b3039>] sysfs_get_dirent+0x29/0x80
[ 128.856495] [<ffffffff811b4d7b>] sysfs_remove_group+0x2b/0x100
[ 128.856626] [<ffffffff81393a20>] xenvbd_sysfs_delif+0x20/0x50
[ 128.856756] [<ffffffff81394518>] xen_blkbk_remove+0xe8/0xf0
[ 128.856895] [<ffffffff8131c768>] xenbus_dev_remove+0x38/0x70
[ 128.857041] [<ffffffff81381601>] __device_release_driver+0x61/0xc0
[ 128.857177] [<ffffffff81381778>] device_release_driver+0x28/0x40
[ 128.857323] [<ffffffff81380896>] bus_remove_device+0x106/0x140
[ 128.857459] [<ffffffff8137e868>] device_del+0x118/0x1c0
[ 128.857580] [<ffffffff8137e921>] device_unregister+0x11/0x20
[ 128.857712] [<ffffffff8139376a>] frontend_changed+0xba/0x350
[ 128.857851] [<ffffffff810337f9>] ? xen_irq_enable_direct_reloc+0x4/0x4
[ 128.857982] [<ffffffff8109928d>] ? finish_task_switch+0x4d/0x100
[ 128.858106] [<ffffffff8131ca18>] xenbus_otherend_changed+0xa8/0xb0
[ 128.858236] [<ffffffff815ab629>] ? _raw_spin_unlock_irqrestore+0x19/0x30
[ 128.858368] [<ffffffff8131cc2b>] frontend_changed+0xb/0x10
[ 128.858522] [<ffffffff8131ad3b>] xenwatch_thread+0xcb/0x190
[ 128.858655] [<ffffffff8108ec40>] ? wake_up_bit+0x40/0x40
[ 128.858801] [<ffffffff8131ac70>] ? xenbus_thread+0x320/0x320
[ 128.858965] [<ffffffff8108e716>] kthread+0x96/0xa0
[ 128.859097] [<ffffffff815b3564>] kernel_thread_helper+0x4/0x10
[ 128.859235] [<ffffffff815abb78>] ? retint_restore_args+0x5/0x6
[ 128.859371] [<ffffffff815b3560>] ? gs_change+0x13/0x13
[ 128.859542] BUG: scheduling while atomic: xenwatch/46/0x00000002

whenever a guest is powered off.

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msw at amazon

Apr 27, 2012, 9:30 AM

Post #4 of 4 (146 views)
Permalink
Re: [RFC] [PATCH] xen/blkback: add locking in statistics sysfs show functions [In reply to]

On Thu, Apr 26, 2012 at 07:24:56PM -0700, Konrad Rzeszutek Wilk wrote:
> On Fri, Apr 20, 2012 at 07:21:13PM +0000, Matt Wilson wrote:
> > This is a port of a patch in the XenoLinux 2.6.18 tree:
> > http://xenbits.xen.org/hg/linux-2.6.18-xen.hg/rev/f47c07325a56
> >
> > Fix blkback sysfs race
>
> So with this patch I keep on getting this:
>
> [ 128.274290] switch: port 2(vif1.0) entered disabled state
...
> [ 128.859542] BUG: scheduling while atomic: xenwatch/46/0x00000002
>
> whenever a guest is powered off.

Oops. I hadn't had a chance to do testing of the patch, I just noticed
that the upstream version didn't have it.

I'll tweak it a bit, do some testing, and resubmit when it works.
--
msw

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