locks: fix tracking of inprogress lease breaks

We currently use a bit in fl_flags to record whether a lease is being
broken, and set fl_type to the type (RDLCK or UNLCK) that it will
eventually have.  This means that once the lease break starts, we forget
what the lease's type *used* to be.  Breaking a read lease will then
result in blocking read opens, even though there's no conflict--because
the lease type is now F_UNLCK and we can no longer tell whether it was
previously a read or write lease.

So, instead keep fl_type as the original type (the type which we
enforce), and keep track of whether we're unlocking or merely
downgrading by replacing the single FL_INPROGRESS flag by
FL_UNLOCK_PENDING and FL_DOWNGRADE_PENDING flags.

To get this right we also need to track separate downgrade and break
times, to handle the case where a write-leased file gets conflicting
opens first for read, then later for write.

(I first considered just eliminating the downgrade behavior
completely--nfsv4 doesn't need it, and nobody as far as I can tell
actually uses it currently--but Jeremy Allison tells me that Windows
oplocks do behave this way, so Samba will probably use this some day.)

Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 327fdd4de85f..76460edf1648 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1065,7 +1065,8 @@ static inline int file_check_writeable(struct file *filp)
 #define FL_LEASE        32      /* lease held on this file */
 #define FL_CLOSE        64      /* unlock on close */
 #define FL_SLEEP        128     /* A blocking lock */
-#define FL_INPROGRESS   256     /* Lease is being broken */
+#define FL_DOWNGRADE_PENDING    256 /* Lease is being downgraded */
+#define FL_UNLOCK_PENDING       512 /* Lease is being broken */
 
 /*
  * Special return value from posix_lock_file() and vfs_lock_file() for
@@ -1122,7 +1123,9 @@ struct file_lock {
         loff_t fl_end;
 
         struct fasync_struct *  fl_fasync; /* for lease break notifications */
-        unsigned long fl_break_time;    /* for nonblocking lease breaks */
+        /* for lease breaks: */
+        unsigned long fl_break_time;
+        unsigned long fl_downgrade_time;
 
         const struct file_lock_operations *fl_ops;      /* Callbacks for filesystems */
         const struct lock_manager_operations *fl_lmops; /* Callbacks for lockmanagers */