linux-kernel - BUG: CGROUPS [2.6.28-rc6] Task migration does not clean reference to group

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <3da2c0120812020100u66a94f9bk3c0e8a705bb6347e@mail.gmail.com>
Date:	Tue, 2 Dec 2008 14:30:14 +0530
From:	"sudhir kumar" <imsudhirkumar@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	vatsa@...ux.vnet.ibm.com, bharata@...ux.vnet.ibm.com,
	dhaval@...ux.vnet.ibm.com, balbir@...ux.vnet.ibm.com,
	skumar@...ux.vnet.ibm.com, Peter <a.p.zijlstra@...llo.nl>,
	"Paul Menage" <menage@...gle.com>, mingo@...e.hu
Subject: BUG: CGROUPS [2.6.28-rc6] Task migration does not clean reference to group

Hi,
I see an interesting bug in the cgroups. I found that cat /proc/cgroups
does not decrease the num_cgroups field when a group is deleted. It looks
to me that somewhere we miss to delete the reference, which leads to a failure
to unmount the cgroups filesystem.
The steps to produce the bug are:

mkdir /cpu
mount -t cgroup -ocpu cgroup /cpu
cd cpu
mkdir group1;
cd group1;
/./while &              # an infinite loop
echo pid > tasks        # pid is of infinite task
cd ..                   # we are now in root group
echo pid > /tasks       # move the task to root group
rmdir group1;           # Succeeds even when I was inside this group
in another shell
cd ..
umount /cpu;    # this fails for me as below
[root@...ik-laptop /]# umount cpu/
umount: cpu/: device is busy

And I see that cat /proc/cgroups shows me still num_cgroups as 2;

I checked it on two kernels.
[root@...ik-laptop cpu]# uname -a
Linux malik-laptop.in.ibm.com 2.6.26 #1 SMP Tue Aug 12 16:39:18 IST
2008 i686 i686 i386 GNU/Linux

[root@...5b sudhir]# uname -a
Linux e325b.in.ibm.com 2.6.28-rc6 #1 SMP Mon Dec 1 15:53:09 IST 2008
i686 athlon i386 GNU/Linux

A look on /proc/cgroups
root@...5b sudhir]# cat /proc/cgroups
#subsys_name    hierarchy       num_cgroups     enabled
#cpuset  0       1       1
#debug   0       1       1
#ns      0       1       1
#cpu     8       2       1
#cpuacct 0       1       1
#freezer 0       1       1
#

Please let me know if further information is required or I am doing
something wrong ?

Thanks
Sudhir
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/