Maneesh Soni wrote:
> On Thu, May 17, 2007 at 05:04:23AM -0700, Greg KH wrote:
>> On Wed, May 16, 2007 at 08:31:00PM +0200, Tejun Heo wrote:
>>> sd->s_dentry updates made by dentry/inode reclamation are racy and can
>>> lead to BUG() or oops. This is already fixed in -mm and the fix is
>>> scheduled to be merged into upstream for 2.6.23 but the fix
>>> reimplements sysfs dentry dropping and is too risky for -stable
>>> kernels.
>>>
>
> But was the synchronization fix tested by people facing the race? I still
> don't understand the racy code path. The last google problem I saw had
> s_dentry field as NULL.
Please take a look at the following message.
http://article.gmane.org/gmane.linux.kernel/521729
I could reproduce both races on my test machine fairly reliable with
parallel find, cat, mount/mount while repeatedly ins/rmmoding a libata
driver.
>>> This is an interim solution for -stable kernels. sysfs reclamation is
>>> disabled by default and can be enabled by using sysfs.enable_reclaim
>>> kernel parameter. Note that dentries are still created on demand, so
>>> attribute and symlinks nodes aren't allocated on creation. They're
>>> allocated on first lookup and deallocated when the sysfs node is
>>> removed.
>> Ick, this is going to kill memory on big boxes (s390 and others) and I
>> don't really want to apply this it if at all possible.
>>
> At least not make it default. This might create boot issues with these
> boxes.
Which makes oopsing the default. Fun! :-)
>> Maneesh, any other thoughts?
>>
> I actually wanted to investigate this oops but left it considering the
> rework being done by Tejun. If this still make sense we can have some
> more debug code stuffed there or get a crashdump (kdump) to get better
> understanding of the race.
The above message contains analysis of both races. I just ported the
fixes. I have a different test machine now and can't reproduce the
races with this one yet so I couldn't verify whether the patches
actually fix the problem. I'll post the patches anyway. If anyone can
reproduce these races, please verify the posted patches fix the problem.
Thanks.
--
tejun
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