kernel/git/stable/linux.git/fs/dcache.c, branch linux-3.5.y

vfs: dcache: fix deadlock in tree traversal

2012-10-07T15:35:49+00:00

commit 8110e16d42d587997bcaee0c864179e6d93603fe upstream. IBM reported a deadlock in select_parent(). This was found to be caused by taking rename_lock when already locked when restarting the tree traversal. There are two cases when the traversal needs to be restarted: 1) concurrent d_move(); this can only happen when not already locked, since taking rename_lock protects against concurrent d_move(). 2) racing with final d_put() on child just at the moment of ascending to parent; rename_lock doesn't protect against this rare race, so it can happen when already locked. Because of case 2, we need to be able to handle restarting the traversal when rename_lock is already held. This patch fixes all three callers of try_to_ascend(). IBM reported that the deadlock is gone with this patch. [ I rewrote the patch to be smaller and just do the "goto again" if the lock was already held, but credit goes to Miklos for the real work. - Linus ] Signed-off-by: Miklos Szeredi Cc: Al Viro Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

vfs: dcache: use DCACHE_DENTRY_KILLED instead of DCACHE_DISCONNECTED in d_kill()

2012-10-02T17:38:58+00:00

commit b161dfa6937ae46d50adce8a7c6b12233e96e7bd upstream. IBM reported a soft lockup after applying the fix for the rename_lock deadlock. Commit c83ce989cb5f ("VFS: Fix the nfs sillyrename regression in kernel 2.6.38") was found to be the culprit. The nfs sillyrename fix used DCACHE_DISCONNECTED to indicate that the dentry was killed. This flag can be set on non-killed dentries too, which results in infinite retries when trying to traverse the dentry tree. This patch introduces a separate flag: DCACHE_DENTRY_KILLED, which is only set in d_kill() and makes try_to_ascend() test only this flag. IBM reported successful test results with this patch. Signed-off-by: Miklos Szeredi Cc: Trond Myklebust Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

Revert "vfs: stop d_splice_alias creating directory aliases"

2012-06-08T17:34:03+00:00

This reverts commit 7732a557b1342c6e6966efb5f07effcf99f56167 (and commit 3f50fff4dace23d3cfeb195d5cd4ee813cee68b7, which was a follow-up cleanup). We're chasing an elusive bug that Dave Jones can apparently reproduce using his system call fuzzer tool, and that looks like some kind of locking ordering problem on the directory i_mutex chain. Our i_mutex locking is rather complex, and depends on the topological ordering of the directories, which is why we have been very wary of splicing directory entries around. Of course, we really don't want to ever see aliased unconnected directories anyway, so none of this should ever happen, but this revert aims to basically get us back to a known older state. Bruce points to some of the previous discussion at http://marc.info/?i=<20110310105821.GE22723@ZenIV.linux.org.uk> and in particular a long post from Neil: http://marc.info/?i=<20110311150749.2fa2be66@notabene.brown> It should be noted that it's possible that Dave's problems come from other changes altohgether, including possibly just the fact that Dave constantly is teachning his fuzzer new tricks. So what appears to be a new bug could in fact be an old one that just gets newly triggered, but reverting these patches as "still under heavy discussion" is the right thing regardless. Requested-by: Al Viro Acked-by: J. Bruce Fields Signed-off-by: Linus Torvalds

vfs: remove unused __d_splice_alias argument

2012-05-31T01:04:54+00:00

Nobody sets want_disconn any more. Reported-by: Peng Tao Signed-off-by: J. Bruce Fields Signed-off-by: Al Viro

vfs: stop d_splice_alias creating directory aliases

2012-05-31T01:04:54+00:00

A directory should never have more than one dentry pointing to it. But d_splice_alias() will add one if it finds a directory with an already-existing non-DISCONNECTED dentry. I can't find an obvious reproducer, but I also can't see what prevents d_splice_alias() from encountering such a case. It therefore seems safest to allow d_splice_alias to use any dentry it finds. (Prior to the removal of dentry_unhash() from vfs_rmdir(), around v3.0, this could cause an nfsd deadlock like this: - Somebody attempts to remove a non-empty directory. - The dentry_unhash() in vfs_rmdir() unhashes the dentry pointing to the non-empty directory. - ->rmdir() then fails with -ENOTEMPTY - Before the vfs_rmdir() caller reaches dput(), an nfsd process in rename looks up the directory by filehandle; at the end of that lookup, this dentry is found by d_alloc_anon(), and a reference is taken on it, preventing dput() from removing it. - A regular lookup of the directory calls d_splice_alias(), finds only an unhashed (not a DISCONNECTED) dentry, and insteads adds a new one, so the directory now has two dentries. - The nfsd process in rename, which was previously looking up the source directory of the rename, now looks up the target directory (which is the same), and gets the dentry newly created by the previous lookup. - The rename, seeing two different dentries, assumes this is a cross-directory rename and attempts to take the i_mutex on the directory twice. That reproducer no longer exists, but I don't think there was anything fundamentally incorrect about the vfs_rmdir() behavior there, so I think the real fault was here in d_splice_alias().) Signed-off-by: J. Bruce Fields Signed-off-by: Al Viro

brlocks/lglocks: API cleanups

2012-05-30T03:28:41+00:00

lglocks and brlocks are currently generated with some complicated macros in lglock.h. But there's no reason to not just use common utility functions and put all the data into a common data structure. In preparation, this patch changes the API to look more like normal function calls with pointers, not magic macros. The patch is rather large because I move over all users in one go to keep it bisectable. This impacts the VFS somewhat in terms of lines changed. But no actual behaviour change. [akpm@linux-foundation.org: checkpatch fixes] Signed-off-by: Andi Kleen Cc: Al Viro Cc: Rusty Russell Signed-off-by: Andrew Morton Signed-off-by: Rusty Russell Signed-off-by: Al Viro

mm: add a low limit to alloc_large_system_hash

2012-05-24T04:28:21+00:00

UDP stack needs a minimum hash size value for proper operation and also uses alloc_large_system_hash() for proper NUMA distribution of its hash tables and automatic sizing depending on available system memory. On some low memory situations, udp_table_init() must ignore the alloc_large_system_hash() result and reallocs a bigger memory area. As we cannot easily free old hash table, we leak it and kmemleak can issue a warning. This patch adds a low limit parameter to alloc_large_system_hash() to solve this problem. We then specify UDP_HTABLE_SIZE_MIN for UDP/UDPLite hash table allocation. Reported-by: Mark Asselstine Reported-by: Tim Bird Signed-off-by: Eric Dumazet Cc: Paul Gortmaker Signed-off-by: David S. Miller

Revert "vfs: remove unnecessary d_unhashed() check from __d_lookup_rcu"

2012-05-22T01:48:10+00:00

This reverts commit 8c01a529b861ba97c7d78368e6a5d4d42e946f75. It turns out the d_unhashed() check isn't unnecessary after all: while it's true that unhashing will increment the sequence numbers, that does not necessarily invalidate the RCU lookup, because it might have seen the dentry pointer (before it got unhashed), but by the time it loaded the sequence number, it could have seen the *new* sequence number (after it got unhashed). End result: we might look up an unhashed dentry that is about to be freed, with the sequence number never indicating anything bad about it. So checking that the dentry is still hashed (*after* reading the sequence number) is indeed the proper fix, and was never unnecessary. Reported-by: Dave Jones Signed-off-by: Linus Torvalds

vfs: be even more careful about dentry RCU name lookups

2012-05-21T23:14:04+00:00

Miklos Szeredi points out that we need to also worry about memory odering when doing the dentry name comparison asynchronously with RCU. In particular, doing a rename can do a memcpy() of one dentry name over another, and we want to make sure that any unlocked reader will always see the proper terminating NUL character, so that it won't ever run off the allocation. Rather than having to be extra careful with the name copy or at lookup time for each character, this resolves the issue by making sure that all names that are inlined in the dentry always have a NUL character at the end of the name allocation. If we do that at dentry allocation time, we know that no future name copy will ever change that final NUL to anything else, so there are no memory ordering issues. So even if a concurrent rename ends up overwriting the NUL character that terminates the original name, we always know that there is one final NUL at the end, and there is no worry about the lockless RCU lookup traversing the name too far. The out-of-line allocations are never copied over, so we can just make sure that we write the name (with terminating NULL) and do a write barrier before we expose the name to anything else by setting it in the dentry. Reported-by: Miklos Szeredi Cc: Al Viro Cc: Nick Piggin Signed-off-by: Linus Torvalds

vfs: make it possible to access the dentry hash/len as one 64-bit entry

2012-05-11T02:54:35+00:00

This allows comparing hash and len in one operation on 64-bit architectures. Right now only __d_lookup_rcu() takes advantage of this, since that is the case we care most about. The use of anonymous struct/unions hides the alternate 64-bit approach from most users, the exception being a few cases where we initialize a 'struct qstr' with a static initializer. This makes the problematic cases use a new QSTR_INIT() helper function for that (but initializing just the name pointer with a "{ .name = xyzzy }" initializer remains valid, as does just copying another qstr structure). Signed-off-by: Linus Torvalds