linux/kernel/cgroup.c, branch v3.6

Merge branch 'for-3.6' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

2012-07-25T00:47:44Z

Pull cgroup changes from Tejun Heo: "Nothing too interesting. A minor bug fix and some cleanups." * 'for-3.6' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup: cgroup: Update remount documentation cgroup: cgroup_rm_files() was calling simple_unlink() with the wrong inode cgroup: Remove populate() documentation cgroup: remove hierarchy_mutex

VFS: Pass mount flags to sget()

2012-07-14T12:38:34Z

Pass mount flags to sget() so that it can use them in initialising a new superblock before the set function is called. They could also be passed to the compare function. Signed-off-by: David Howells Signed-off-by: Al Viro

stop passing nameidata to ->lookup()

2012-07-14T12:34:32Z

Just the flags; only NFS cares even about that, but there are legitimate uses for such argument. And getting rid of that completely would require splitting ->lookup() into a couple of methods (at least), so let's leave that alone for now... Signed-off-by: Al Viro

cgroup: cgroup_rm_files() was calling simple_unlink() with the wrong inode

2012-07-09T17:11:14Z

While refactoring cgroup file removal path, 05ef1d7c4a "cgroup: introduce struct cfent" incorrectly changed the @dir argument of simple_unlink() to the inode of the file being deleted instead of that of the containing directory. The effect of this bug is minor - ctime and mtime of the parent weren't properly updated on file deletion. Fix it by using @cgrp->dentry->d_inode instead. Signed-off-by: Tejun Heo Reported-by: Al Viro Acked-by: Li Zefan Cc: stable@vger.kernel.org

cgroup: fix cgroup hierarchy umount race

2012-07-07T23:08:18Z

48ddbe1946 "cgroup: make css->refcnt clearing on cgroup removal optional" allowed a css to linger after the associated cgroup is removed. As a css holds a reference on the cgroup's dentry, it means that cgroup dentries may linger for a while. Destroying a superblock which has dentries with positive refcnts is a critical bug and triggers BUG() in vfs code. As each cgroup dentry holds an s_active reference, any lingering cgroup has both its dentry and the superblock pinned and thus preventing premature release of superblock. Unfortunately, after 48ddbe1946, there's a small window while releasing a cgroup which is directly under the root of the hierarchy. When a cgroup directory is released, vfs layer first deletes the corresponding dentry and then invokes dput() on the parent, which may recurse further, so when a cgroup directly below root cgroup is released, the cgroup is first destroyed - which releases the s_active it was holding - and then the dentry for the root cgroup is dput(). This creates a window where the root dentry's refcnt isn't zero but superblock's s_active is. If umount happens before or during this window, vfs will see the root dentry with non-zero refcnt and trigger BUG(). Before 48ddbe1946, this problem didn't exist because the last dentry reference was guaranteed to be put synchronously from rmdir(2) invocation which holds s_active around the whole process. Fix it by holding an extra superblock->s_active reference across dput() from css release, which is the dput() path added by 48ddbe1946 and the only one which doesn't hold an extra s_active ref across the final cgroup dput(). Signed-off-by: Tejun Heo LKML-Reference: <4FEEA5CB.8070809@huawei.com> Reported-by: shyju pv Tested-by: shyju pv Cc: Sasha Levin Acked-by: Li Zefan

Revert "cgroup: superblock can't be released with active dentries"

2012-07-07T22:55:47Z

This reverts commit fa980ca87d15bb8a1317853f257a505990f3ffde. The commit was an attempt to fix a race condition where a cgroup hierarchy may be unmounted with positive dentry reference on root cgroup. While the commit made the race condition slightly more difficult to trigger, the race was still there and could be reliably triggered using a different test case. Revert the incorrect fix. The next commit will describe the race and fix it correctly. Signed-off-by: Tejun Heo LKML-Reference: <4FEEA5CB.8070809@huawei.com> Reported-by: shyju pv Cc: Sasha Levin Acked-by: Li Zefan

cgroups: Account for CSS_DEACT_BIAS in __css_put

2012-06-18T22:38:02Z

When we fixed the race between atomic_dec and css_refcnt, we missed the fact that css_refcnt internally subtracts CSS_DEACT_BIAS to get the actual reference count. This can potentially cause a refcount leak if __css_put races with cgroup_clear_css_refs. Signed-off-by: Salman Qazi Acked-by: Li Zefan Signed-off-by: Tejun Heo

cgroup: remove hierarchy_mutex

2012-06-07T02:12:30Z

It was introduced for memcg to iterate cgroup hierarchy without holding cgroup_mutex, but soon after that it was replaced with a lockless way in memcg. No one used hierarchy_mutex since that, so remove it. Signed-off-by: Li Zefan Signed-off-by: Tejun Heo

cgroup: make sure that decisions in __css_put are atomic

2012-06-07T01:51:35Z

__css_put is using atomic_dec on the ref count, and then looking at the ref count to make decisions. This is prone to races, as someone else may decrement ref count between our decrement and our decision. Instead, we should base our decisions on the value that we decremented the ref count to. (This results in an actual race on Google's kernel which I haven't been able to reproduce on the upstream kernel. Having said that, it's still incorrect by inspection). Signed-off-by: Salman Qazi Acked-by: Li Zefan Signed-off-by: Tejun Heo Cc: stable@vger.kernel.org

Merge branch 'for-3.5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

2012-06-05T18:54:12Z

Pull cgroup fix from Tejun Heo: "This fixes the possible premature superblock release on umount bug mentioned during v3.5-rc1 pull request. Originally, cgroup dentry destruction path assumed that cgroup dentry didn't have any reference left after cgroup removal thus put super during dentry removal. Now that there can be lingering dentry references, this led to super being put with live dentries. This patch fixes the problem by putting super ref on dentry release instead of removal." * 'for-3.5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup: cgroup: superblock can't be released with active dentries