linux-stable.git/fs/proc/inode.c, branch linux-3.2.y

vfs,proc: guarantee unique inodes in /proc

2013-03-27T02:41:23+00:00

commit 51f0885e5415b4cc6535e9cdcc5145bfbc134353 upstream.

Dave Jones found another /proc issue with his Trinity tool: thanks to
the namespace model, we can have multiple /proc dentries that point to
the same inode, aliasing directories in /proc//net/ for example.

This ends up being a total disaster, because it acts like hardlinked
directories, and causes locking problems.  We rely on the topological
sort of the inodes pointed to by dentries, and if we have aliased
directories, that odering becomes unreliable.

In short: don't do this.  Multiple dentries with the same (directory)
inode is just a bad idea, and the namespace code should never have
exposed things this way.  But we're kind of stuck with it.

This solves things by just always allocating a new inode during /proc
dentry lookup, instead of using "iget_locked()" to look up existing
inodes by superblock and number.  That actually simplies the code a bit,
at the cost of potentially doing more inode [de]allocations.

That said, the inode lookup wasn't free either (and did a lot of locking
of inodes), so it is probably not that noticeable.  We could easily keep
the old lookup model for non-directory entries, but rather than try to
be excessively clever this just implements the minimal and simplest
workaround for the problem.

Reported-and-tested-by: Dave Jones 
Analyzed-by: Al Viro 
Signed-off-by: Linus Torvalds 
[bwh: Backported to 3.2:
 - Adjust context
 - Never drop the pde reference in proc_get_inode(), as callers only
   expect this when we return an existing inode, and we never do that now]
Signed-off-by: Ben Hutchings

filesystems: add set_nlink()

2011-11-02T11:53:43+00:00

Replace remaining direct i_nlink updates with a new set_nlink()
updater function.

Signed-off-by: Miklos Szeredi 
Tested-by: Toshiyuki Okajima 
Signed-off-by: Christoph Hellwig

procfs: return ENOENT on opening a being-removed proc entry

2011-07-26T23:49:43+00:00

Change the return value to ENOENT.  This return value is then returned
when opening the proc entry that have been removed.  For example,
open("/proc/bus/pci/XX/YY") when the corresponding device is being
hot-removed.

Signed-off-by: Daisuke Ogino 
Cc: Jesse Barnes 
Acked-by: Alexey Dobriyan 
Cc: Christoph Hellwig 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

ns: proc files for namespace naming policy.

2011-05-10T21:31:44+00:00

Create files under /proc//ns/ to allow controlling the
namespaces of a process.

This addresses three specific problems that can make namespaces hard to
work with.
- Namespaces require a dedicated process to pin them in memory.
- It is not possible to use a namespace unless you are the child
  of the original creator.
- Namespaces don't have names that userspace can use to talk about
  them.

The namespace files under /proc//ns/ can be opened and the
file descriptor can be used to talk about a specific namespace, and
to keep the specified namespace alive.

A namespace can be kept alive by either holding the file descriptor
open or bind mounting the file someplace else.  aka:
mount --bind /proc/self/ns/net /some/filesystem/path
mount --bind /proc/self/fd/ /some/filesystem/path

This allows namespaces to be named with userspace policy.

It requires additional support to make use of these filedescriptors
and that will be comming in the following patches.

Acked-by: Daniel Lezcano 
Signed-off-by: Eric W. Biederman

procfs: kill the global proc_mnt variable

2011-03-24T02:46:58+00:00

After the previous cleanup in proc_get_sb() the global proc_mnt has no
reasons to exists, kill it.

Signed-off-by: Oleg Nesterov 
Signed-off-by: Eric W. Biederman 
Signed-off-by: Daniel Lezcano 
Cc: Alexey Dobriyan 
Acked-by: Serge E. Hallyn 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

unfuck proc_sysctl ->d_compare()

2011-03-08T07:22:27+00:00

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

proc: ->low_ino cleanup

2011-01-13T16:03:16+00:00

- ->low_ino is write-once field -- reading it under locks is unnecessary.

- /proc/$PID stuff never reaches pde_put()/free_proc_entry() --
   PROC_DYNAMIC_FIRST check never triggers.

- in proc_get_inode(), inode number always matches proc dir entry, so
  save one parameter.

Signed-off-by: Alexey Dobriyan 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fs: icache RCU free inodes

2011-01-07T06:50:26+00:00

RCU free the struct inode. This will allow:

- Subsequent store-free path walking patch. The inode must be consulted for
  permissions when walking, so an RCU inode reference is a must.
- sb_inode_list_lock to be moved inside i_lock because sb list walkers who want
  to take i_lock no longer need to take sb_inode_list_lock to walk the list in
  the first place. This will simplify and optimize locking.
- Could remove some nested trylock loops in dcache code
- Could potentially simplify things a bit in VM land. Do not need to take the
  page lock to follow page->mapping.

The downsides of this is the performance cost of using RCU. In a simple
creat/unlink microbenchmark, performance drops by about 10% due to inability to
reuse cache-hot slab objects. As iterations increase and RCU freeing starts
kicking over, this increases to about 20%.

In cases where inode lifetimes are longer (ie. many inodes may be allocated
during the average life span of a single inode), a lot of this cache reuse is
not applicable, so the regression caused by this patch is smaller.

The cache-hot regression could largely be avoided by using SLAB_DESTROY_BY_RCU,
however this adds some complexity to list walking and store-free path walking,
so I prefer to implement this at a later date, if it is shown to be a win in
real situations. I haven't found a regression in any non-micro benchmark so I
doubt it will be a problem.

Signed-off-by: Nick Piggin

BKL: remove extraneous #include

2010-11-17T16:59:32+00:00

The big kernel lock has been removed from all these files at some point,
leaving only the #include.

Remove this too as a cleanup.

Signed-off-by: Arnd Bergmann 
Signed-off-by: Linus Torvalds

bkl: Remove locked .ioctl file operation

2010-08-13T22:24:24+00:00

The last user is gone, so we can safely remove this

Signed-off-by: Arnd Bergmann 
Cc: John Kacur 
Cc: Al Viro 
Cc: Thomas Gleixner 
Signed-off-by: Frederic Weisbecker