linux/fs/proc/proc_sysctl.c, branch v3.0.56

proc_sys_permission() is OK in RCU mode

2011-06-20T14:45:25Z

nothing blocking there, since all instances of sysctl ->permissions() method are non-blocking - both of them, that is. Signed-off-by: Al Viro

Merge branch 'next' into for-linus

2011-03-15T22:41:17Z

unfuck proc_sysctl ->d_compare()

2011-03-08T07:22:27Z

a) struct inode is not going to be freed under ->d_compare(); however, the thing PROC_I(inode)->sysctl points to just might. Fortunately, it's enough to make freeing that sucker delayed, provided that we don't step on its ->unregistering, clear the pointer to it in PROC_I(inode) before dropping the reference and check if it's NULL in ->d_compare(). b) I'm not sure that we *can* walk into NULL inode here (we recheck dentry->seq between verifying that it's still hashed / fetching dentry->d_inode and passing it to ->d_compare() and there's no negative hashed dentries in /proc/sys/*), but if we can walk into that, we really should not have ->d_compare() return 0 on it! Said that, I really suspect that this check can be simply killed. Nick? Signed-off-by: Al Viro

security/selinux: fix /proc/sys/ labeling

2011-02-01T16:53:54Z

This fixes an old (2007) selinux regression: filesystem labeling for /proc/sys returned -r--r--r-- unknown /proc/sys/fs/file-nr instead of -r--r--r-- system_u:object_r:sysctl_fs_t:s0 /proc/sys/fs/file-nr Events that lead to breaking of /proc/sys/ selinux labeling: 1) sysctl was reimplemented to route all calls through /proc/sys/ commit 77b14db502cb85a031fe8fde6c85d52f3e0acb63 [PATCH] sysctl: reimplement the sysctl proc support 2) proc_dir_entry was removed from ctl_table: commit 3fbfa98112fc3962c416452a0baf2214381030e6 [PATCH] sysctl: remove the proc_dir_entry member for the sysctl tables 3) selinux still walked the proc_dir_entry tree to apply labeling. Because ctl_tables don't have a proc_dir_entry, we did not label /proc/sys/ inodes any more. To achieve this the /proc/sys/ inodes were marked private and private inodes were ignored by selinux. commit bbaca6c2e7ef0f663bc31be4dad7cf530f6c4962 [PATCH] selinux: enhance selinux to always ignore private inodes commit 86a71dbd3e81e8870d0f0e56b87875f57e58222b [PATCH] sysctl: hide the sysctl proc inodes from selinux Access control checks have been done by means of a special sysctl hook that was called for read/write accesses to any /proc/sys/ entry. We don't have to do this because, instead of walking the proc_dir_entry tree we can walk the dentry tree (as done in this patch). With this patch: * we don't mark /proc/sys/ inodes as private * we don't need the sysclt security hook * we walk the dentry tree to find the path to the inode. We have to strip the PID in /proc/PID/ entries that have a proc_dir_entry because selinux does not know how to label paths like '/1/net/rpc/nfsd.fh' (and defaults to 'proc_t' labeling). Selinux does know of '/net/rpc/nfsd.fh' (and applies the 'sysctl_rpc_t' label). PID stripping from the path was done implicitly in the previous code because the proc_dir_entry tree had the root in '/net' in the example from above. The dentry tree has the root in '/1'. Signed-off-by: Eric W. Biederman Signed-off-by: Lucian Adrian Grijincu Signed-off-by: Eric Paris

fs: provide rcu-walk aware permission i_ops

2011-01-07T06:50:29Z

Signed-off-by: Nick Piggin

fs: rcu-walk aware d_revalidate method

2011-01-07T06:50:29Z

Require filesystems be aware of .d_revalidate being called in rcu-walk mode (nd->flags & LOOKUP_RCU). For now do a simple push down, returning -ECHILD from all implementations. Signed-off-by: Nick Piggin

fs: dcache reduce branches in lookup path

2011-01-07T06:50:28Z

Reduce some branches and memory accesses in dcache lookup by adding dentry flags to indicate common d_ops are set, rather than having to check them. This saves a pointer memory access (dentry->d_op) in common path lookup situations, and saves another pointer load and branch in cases where we have d_op but not the particular operation. Patched with: git grep -E '[.>]([[:space:]])*d_op([[:space:]])*=' | xargs sed -e 's/\([^\t ]*\)->d_op = \(.*\);/d_set_d_op(\1, \2);/' -e 's/\([^\t ]*\)\.d_op = \(.*\);/d_set_d_op(\&\1, \2);/' -i Signed-off-by: Nick Piggin

fs: rcu-walk for path lookup

2011-01-07T06:50:27Z

Perform common cases of path lookups without any stores or locking in the ancestor dentry elements. This is called rcu-walk, as opposed to the current algorithm which is a refcount based walk, or ref-walk. This results in far fewer atomic operations on every path element, significantly improving path lookup performance. It also avoids cacheline bouncing on common dentries, significantly improving scalability. The overall design is like this: * LOOKUP_RCU is set in nd->flags, which distinguishes rcu-walk from ref-walk. * Take the RCU lock for the entire path walk, starting with the acquiring of the starting path (eg. root/cwd/fd-path). So now dentry refcounts are not required for dentry persistence. * synchronize_rcu is called when unregistering a filesystem, so we can access d_ops and i_ops during rcu-walk. * Similarly take the vfsmount lock for the entire path walk. So now mnt refcounts are not required for persistence. Also we are free to perform mount lookups, and to assume dentry mount points and mount roots are stable up and down the path. * Have a per-dentry seqlock to protect the dentry name, parent, and inode, so we can load this tuple atomically, and also check whether any of its members have changed. * Dentry lookups (based on parent, candidate string tuple) recheck the parent sequence after the child is found in case anything changed in the parent during the path walk. * inode is also RCU protected so we can load d_inode and use the inode for limited things. * i_mode, i_uid, i_gid can be tested for exec permissions during path walk. * i_op can be loaded. When we reach the destination dentry, we lock it, recheck lookup sequence, and increment its refcount and mountpoint refcount. RCU and vfsmount locks are dropped. This is termed "dropping rcu-walk". If the dentry refcount does not match, we can not drop rcu-walk gracefully at the current point in the lokup, so instead return -ECHILD (for want of a better errno). This signals the path walking code to re-do the entire lookup with a ref-walk. Aside from the final dentry, there are other situations that may be encounted where we cannot continue rcu-walk. In that case, we drop rcu-walk (ie. take a reference on the last good dentry) and continue with a ref-walk. Again, if we can drop rcu-walk gracefully, we return -ECHILD and do the whole lookup using ref-walk. But it is very important that we can continue with ref-walk for most cases, particularly to avoid the overhead of double lookups, and to gain the scalability advantages on common path elements (like cwd and root). The cases where rcu-walk cannot continue are: * NULL dentry (ie. any uncached path element) * parent with d_inode->i_op->permission or ACLs * dentries with d_revalidate * Following links In future patches, permission checks and d_revalidate become rcu-walk aware. It may be possible eventually to make following links rcu-walk aware. Uncached path elements will always require dropping to ref-walk mode, at the very least because i_mutex needs to be grabbed, and objects allocated. Signed-off-by: Nick Piggin

fs: change d_compare for rcu-walk

2011-01-07T06:50:19Z

Change d_compare so it may be called from lock-free RCU lookups. This does put significant restrictions on what may be done from the callback, however there don't seem to have been any problems with in-tree fses. If some strange use case pops up that _really_ cannot cope with the rcu-walk rules, we can just add new rcu-unaware callbacks, which would cause name lookup to drop out of rcu-walk mode. For in-tree filesystems, this is just a mechanical change. Signed-off-by: Nick Piggin

fs: change d_delete semantics

2011-01-07T06:50:18Z

Change d_delete from a dentry deletion notification to a dentry caching advise, more like ->drop_inode. Require it to be constant and idempotent, and not take d_lock. This is how all existing filesystems use the callback anyway. This makes fine grained dentry locking of dput and dentry lru scanning much simpler. Signed-off-by: Nick Piggin