kernel.git/fs/nfs/dir.c, branch linux-3.17.y

NFS: fix two problems in lookup_revalidate in RCU-walk

2014-08-04T13:22:08Z

1/ rcu_dereference isn't correct: that field isn't RCU protected. It could potentially change at any time so ACCESS_ONCE might be justified. changes to ->d_parent are protected by ->d_seq. However that isn't always checked after ->d_revalidate is called, so it is safest to keep the double-check that ->d_parent hasn't changed at the end of these functions. 2/ in nfs4_lookup_revalidate, "->d_parent" was forgotten. So 'parent' was not the parent of 'dentry'. This fails safe is the context is that dentry->d_inode is NULL, and the result of parent->d_inode being NULL is that ECHILD is returned, which is always safe. Reported-by: kbuild test robot Signed-off-by: NeilBrown Signed-off-by: Trond Myklebust

NFS: allow lockless access to access_cache

2014-08-03T21:14:13Z

The access cache is used during RCU-walk path lookups, so it is best to avoid locking if possible as taking a lock kills concurrency. The rbtree is not rcu-safe and cannot easily be made so. Instead we simply check the last (i.e. most recent) entry on the LRU list. If this doesn't match, then we return -ECHILD and retry in lock/refcount mode. This requires freeing the nfs_access_entry struct with rcu, and requires using rcu access primatives when adding entries to the lru, and when examining the last entry. Calling put_rpccred before kfree_rcu looks a bit odd, but as put_rpccred already provides rcu protection, we know that the cred will not actually be freed until the next grace period, so any concurrent access will be safe. This patch provides about 5% performance improvement on a stat-heavy synthetic work load with 4 threads on a 2-core CPU. Signed-off-by: NeilBrown Signed-off-by: Trond Myklebust

NFS: teach nfs_lookup_verify_inode to handle LOOKUP_RCU

2014-08-03T21:14:13Z

It fails with -ECHILD rather than make an RPC call. This allows nfs_lookup_revalidate to call it in RCU-walk mode. Signed-off-by: NeilBrown Signed-off-by: Trond Myklebust

NFS: teach nfs_neg_need_reval to understand LOOKUP_RCU

2014-08-03T21:14:12Z

This requires nfs_check_verifier to take an rcu_walk flag, and requires an rcu version of nfs_revalidate_inode which returns -ECHILD rather than making an RPC call. With this, nfs_lookup_revalidate can call nfs_neg_need_reval in RCU-walk mode. We can also move the LOOKUP_RCU check past the nfs_check_verifier() call in nfs_lookup_revalidate. If RCU_WALK prevents nfs_check_verifier or nfs_neg_need_reval from doing a full check, they return a status indicating that a revalidation is required. As this revalidation will not be possible in RCU_WALK mode, -ECHILD will ultimately be returned, which is the desired result. Signed-off-by: NeilBrown Signed-off-by: Trond Myklebust

NFS: support RCU_WALK in nfs_permission()

2014-08-03T21:14:12Z

nfs_permission makes two calls which are not always safe in RCU_WALK, rpc_lookup_cred and nfs_do_access. The second can easily be made rcu-safe by aborting with -ECHILD before making the RPC call. The former can be made rcu-safe by calling rpc_lookup_cred_nonblock() instead. As this will almost always succeed, we use it even when RCU_WALK isn't being used as it still saves some spinlocks in a common case. We only fall back to rpc_lookup_cred() if rpc_lookup_cred_nonblock() fails and MAY_NOT_BLOCK isn't set. This optimisation (always trying rpc_lookup_cred_nonblock()) is particularly important when a security module is active. In that case inode_permission() may return -ECHILD from security_inode_permission() even though ->permission() succeeded in RCU_WALK mode. This leads to may_lookup() retrying inode_permission after performing unlazy_walk(). The spinlock that rpc_lookup_cred() takes is often more expensive than anything security_inode_permission() does, so that spinlock becomes the main bottleneck. Signed-off-by: NeilBrown Signed-off-by: Trond Myklebust

NFS: prepare for RCU-walk support but pushing tests later in code.

2014-08-03T21:14:11Z

nfs_lookup_revalidate, nfs4_lookup_revalidate, and nfs_permission all need to understand and handle RCU-walk for NFS to gain the benefits of RCU-walk for cached information. Currently these functions all immediately return -ECHILD if the relevant flag (LOOKUP_RCU or MAY_NOT_BLOCK) is set. This patch pushes those tests later in the code so that we only abort immediately before we enter rcu-unsafe code. As subsequent patches make that rcu-unsafe code rcu-safe, several of these new tests will disappear. With this patch there are several paths through the code which will no longer return -ECHILD during an RCU-walk. However these are mostly error paths or other uninteresting cases. A noteworthy change in nfs_lookup_revalidate is that we don't take (or put) the reference to ->d_parent when LOOKUP_RCU is set. Rather we rcu_dereference ->d_parent, and check that ->d_inode is not NULL. We also check that ->d_parent hasn't changed after all the tests. In nfs4_lookup_revalidate we simply avoid testing LOOKUP_RCU on the path that only calls nfs_lookup_revalidate() as that function already performs the required test. Signed-off-by: NeilBrown Signed-off-by: Trond Myklebust

NFS: nfs4_lookup_revalidate: only evaluate parent if it will be used.

2014-08-03T21:14:11Z

nfs4_lookup_revalidate only uses 'parent' to get 'dir', and only uses 'dir' if 'inode == NULL'. So we don't need to find out what 'parent' or 'dir' is until we know that 'inode' is NULL. By moving 'dget_parent' inside the 'if', we can reduce the number of call sites for 'dput(parent)'. Signed-off-by: NeilBrown Signed-off-by: Trond Myklebust

NFS: Enforce an upper limit on the number of cached access call

2014-08-03T21:03:22Z

This may be used to limit the number of cached credentials building up inside the access cache. Signed-off-by: Trond Myklebust

arch: Mass conversion of smp_mb__*()

2014-04-18T12:20:48Z

Mostly scripted conversion of the smp_mb__* barriers. Signed-off-by: Peter Zijlstra Acked-by: Paul E. McKenney Link: http://lkml.kernel.org/n/tip-55dhyhocezdw1dg7u19hmh1u@git.kernel.org Cc: Linus Torvalds Cc: linux-arch@vger.kernel.org Signed-off-by: Ingo Molnar

Merge tag 'nfs-for-3.15-1' of git://git.linux-nfs.org/projects/trondmy/linux-nfs

2014-04-06T17:09:38Z

Pull NFS client updates from Trond Myklebust: "Highlights include: - Stable fix for a use after free issue in the NFSv4.1 open code - Fix the SUNRPC bi-directional RPC code to account for TCP segmentation - Optimise usage of readdirplus when confronted with 'ls -l' situations - Soft mount bugfixes - NFS over RDMA bugfixes - NFSv4 close locking fixes - Various NFSv4.x client state management optimisations - Rename/unlink code cleanups" * tag 'nfs-for-3.15-1' of git://git.linux-nfs.org/projects/trondmy/linux-nfs: (28 commits) nfs: pass string length to pr_notice message about readdir loops NFSv4: Fix a use-after-free problem in open() SUNRPC: rpc_restart_call/rpc_restart_call_prepare should clear task->tk_status SUNRPC: Don't let rpc_delay() clobber non-timeout errors SUNRPC: Ensure call_connect_status() deals correctly with SOFTCONN tasks SUNRPC: Ensure call_status() deals correctly with SOFTCONN tasks NFSv4: Ensure we respect soft mount timeouts during trunking discovery NFSv4: Schedule recovery if nfs40_walk_client_list() is interrupted NFS: advertise only supported callback netids SUNRPC: remove KERN_INFO from dprintk() call sites SUNRPC: Fix large reads on NFS/RDMA NFS: Clean up: revert increase in READDIR RPC buffer max size SUNRPC: Ensure that call_bind times out correctly SUNRPC: Ensure that call_connect times out correctly nfs: emit a fsnotify_nameremove call in sillyrename codepath nfs: remove synchronous rename code nfs: convert nfs_rename to use async_rename infrastructure nfs: make nfs_async_rename non-static nfs: abstract out code needed to complete a sillyrename NFSv4: Clear the open state flags if the new stateid does not match ...