From ab2af1f5005069321c5d130f09cce577b03f43ef Mon Sep 17 00:00:00 2001 From: Dipankar Sarma Date: Fri, 9 Sep 2005 13:04:13 -0700 Subject: [PATCH] files: files struct with RCU Patch to eliminate struct files_struct.file_lock spinlock on the reader side and use rcu refcounting rcuref_xxx api for the f_count refcounter. The updates to the fdtable are done by allocating a new fdtable structure and setting files->fdt to point to the new structure. The fdtable structure is protected by RCU thereby allowing lock-free lookup. For fd arrays/sets that are vmalloced, we use keventd to free them since RCU callbacks can't sleep. A global list of fdtable to be freed is not scalable, so we use a per-cpu list. If keventd is already handling the current cpu's work, we use a timer to defer queueing of that work. Since the last publication, this patch has been re-written to avoid using explicit memory barriers and use rcu_assign_pointer(), rcu_dereference() premitives instead. This required that the fd information is kept in a separate structure (fdtable) and updated atomically. Signed-off-by: Dipankar Sarma Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/open.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'fs/open.c') diff --git a/fs/open.c b/fs/open.c index b6542516a0ca..2fac58c51910 100644 --- a/fs/open.c +++ b/fs/open.c @@ -24,6 +24,7 @@ #include #include #include +#include #include @@ -930,9 +931,8 @@ void fastcall fd_install(unsigned int fd, struct file * file) struct fdtable *fdt; spin_lock(&files->file_lock); fdt = files_fdtable(files); - if (unlikely(fdt->fd[fd] != NULL)) - BUG(); - fdt->fd[fd] = file; + BUG_ON(fdt->fd[fd] != NULL); + rcu_assign_pointer(fdt->fd[fd], file); spin_unlock(&files->file_lock); } @@ -1024,7 +1024,7 @@ asmlinkage long sys_close(unsigned int fd) filp = fdt->fd[fd]; if (!filp) goto out_unlock; - fdt->fd[fd] = NULL; + rcu_assign_pointer(fdt->fd[fd], NULL); FD_CLR(fd, fdt->close_on_exec); __put_unused_fd(files, fd); spin_unlock(&files->file_lock); -- cgit v1.2.3