[PATCH v1 00/12] vfs: add the ability to retry on ESTALE to several syscalls

[PATCH v1 00/12] vfs: add the ability to retry on ESTALE to several syscalls

[Jeff Layton]

ESTALE errors are a source of pain for many users, primarily those who
are doing work on NFS. When userspace provides a path to a syscall, then
there's really little excuse for returning ESTALE. If userspace gave us
a path that we had to lookup in order to do the call, then it's not
particularly helpful to return ESTALE just because that path went stale
before we could do the actual operation.

We can and should do better here. The kernel should instead catch that
error and retry the lookup and call, while forcing a revalidation of all
dentries involved.

Unfortunately fixing this requires touching the syscalls themselves, or
at least their immediate helper functions. Not all syscalls can be
retried -- only those that take a pathname as an argument.

This set is a first "official" pass at adding ESTALE retry handling to
various syscalls.  With this patchset, I've decided to take the
relatively less controversial approach of just having the kernel retry
once when it gets an ESTALE error. I still think that it's not as strong
as it should be, but it should improve the situation in many common
cases.

I've also tried to engineer this in such a way that if we do decide that
we need to retry more than once, then it should be easy to change that
later. This should cover all of the syscalls in fs/stat.c and
fs/namei.c.

If this approach is reasonable I'll look at adding similar handling to
other path-based vfs calls in a another set. A quick look shows that
we have about 50-odd path-based syscalls that will need similar
handling, so this is just a start.

Comments welcome...

Jeff Layton (12):
  vfs: add a retry_estale helper function to handle retries on ESTALE
  vfs: make fstatat retry on ESTALE errors from getattr call
  vfs: fix readlinkat to retry on ESTALE
  vfs: add new "reval" argument to kern_path_create and
    user_path_create
  vfs: fix mknodat to retry on ESTALE errors
  vfs: fix mkdir to retry on ESTALE errors
  vfs: add a "reval" flag to args for user_path_parent
  vfs: make rmdir retry on ESTALE errors
  vfs: make do_unlinkat retry on ESTALE errors
  vfs: fix symlinkat to retry on ESTALE errors
  vfs: fix linkat to retry on ESTALE errors
  vfs: fix renameat to retry on ESTALE errors

 arch/powerpc/platforms/cell/spufs/syscalls.c |    2 +-
 drivers/base/devtmpfs.c                      |    7 +-
 fs/namei.c                                   |  233 +++++++++++++++-----------
 fs/ocfs2/refcounttree.c                      |    3 +-
 fs/stat.c                                    |   32 +++-
 include/linux/fs.h                           |   21 +++
 include/linux/namei.h                        |    4 +-
 net/unix/af_unix.c                           |    3 +-
 8 files changed, 191 insertions(+), 114 deletions(-)

-- 
1.7.7.6

[PATCH v1 01/12] vfs: add a retry_estale helper function to handle retries on ESTALE

[Jeff Layton]

This function is expected to be called from path-based syscalls to help
them decide whether to try the lookup and call again in the event that
they got an -ESTALE return back on an earier try.

Currently, we only retry the call once on an ESTALE error, but in the
event that we decide that that's not enough in the future, we should be
able to change the logic in this helper without too much effort.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 include/linux/fs.h |   21 +++++++++++++++++++++
 1 files changed, 21 insertions(+), 0 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 8de6755..3c0bcda 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2026,6 +2026,27 @@ extern struct file * dentry_open(struct dentry *, struct vfsmount *, int,
 extern int filp_close(struct file *, fl_owner_t id);
 extern char * getname(const char __user *);
 
+/**
+ * retry_estale - determine whether the caller should retry an operation
+ *
+ * @error: the error we'll be returning
+ * @try: number of retries already performed
+ *
+ * Check to see if the error code was -ESTALE, and then determine whether
+ * to retry the call based on the number of retries so far. Currently, we only
+ * retry the call once.
+ *
+ * Returns true if the caller should try again.
+ */
+static inline bool
+retry_estale(const long error, const unsigned int try)
+{
+	if (likely(error != -ESTALE))
+		return false;
+
+	return !try;
+}
+
 /* fs/ioctl.c */
 
 extern int ioctl_preallocate(struct file *filp, void __user *argp);
-- 
1.7.7.6