tree 73a70ba486f522cd9eeeef376ede2b5a1c1b473b
parent 6e72ad2c581de121cc7e772469e2a8f6b1fd4379
author Dipankar Sarma <[EMAIL PROTECTED]> Sat, 10 Sep 2005 03:04:13 -0700
committer Linus Torvalds <[EMAIL PROTECTED]> Sat, 10 Sep 2005 03:57:55 -0700

[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 <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>

 fs/aio.c                  |    3 
 fs/fcntl.c                |   13 +
 fs/file.c                 |  391 ++++++++++++++++++++++++++++++----------------
 fs/file_table.c           |   40 +++-
 fs/open.c                 |    8 
 include/linux/file.h      |   11 +
 include/linux/fs.h        |    4 
 include/linux/init_task.h |    5 
 kernel/exit.c             |   15 -
 kernel/fork.c             |   23 ++
 10 files changed, 346 insertions(+), 167 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -29,6 +29,7 @@
 #include <linux/highmem.h>
 #include <linux/workqueue.h>
 #include <linux/security.h>
+#include <linux/rcuref.h>
 
 #include <asm/kmap_types.h>
 #include <asm/uaccess.h>
@@ -499,7 +500,7 @@ static int __aio_put_req(struct kioctx *
        /* Must be done under the lock to serialise against cancellation.
         * Call this aio_fput as it duplicates fput via the fput_work.
         */
-       if (unlikely(atomic_dec_and_test(&req->ki_filp->f_count))) {
+       if (unlikely(rcuref_dec_and_test(&req->ki_filp->f_count))) {
                get_ioctx(ctx);
                spin_lock(&fput_lock);
                list_add(&req->ki_list, &fput_head);
diff --git a/fs/fcntl.c b/fs/fcntl.c
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -16,6 +16,7 @@
 #include <linux/security.h>
 #include <linux/ptrace.h>
 #include <linux/signal.h>
+#include <linux/rcupdate.h>
 
 #include <asm/poll.h>
 #include <asm/siginfo.h>
@@ -64,8 +65,8 @@ static int locate_fd(struct files_struct
        if (orig_start >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur)
                goto out;
 
-       fdt = files_fdtable(files);
 repeat:
+       fdt = files_fdtable(files);
        /*
         * Someone might have closed fd's in the range
         * orig_start..fdt->next_fd
@@ -95,9 +96,15 @@ repeat:
        if (error)
                goto repeat;
 
+       /*
+        * We reacquired files_lock, so we are safe as long as
+        * we reacquire the fdtable pointer and use it while holding
+        * the lock, no one can free it during that time.
+        */
+       fdt = files_fdtable(files);
        if (start <= fdt->next_fd)
                fdt->next_fd = newfd + 1;
-       
+
        error = newfd;
        
 out:
@@ -163,7 +170,7 @@ asmlinkage long sys_dup2(unsigned int ol
        if (!tofree && FD_ISSET(newfd, fdt->open_fds))
                goto out_fput;
 
-       fdt->fd[newfd] = file;
+       rcu_assign_pointer(fdt->fd[newfd], file);
        FD_SET(newfd, fdt->open_fds);
        FD_CLR(newfd, fdt->close_on_exec);
        spin_unlock(&files->file_lock);
diff --git a/fs/file.c b/fs/file.c
--- a/fs/file.c
+++ b/fs/file.c
@@ -13,6 +13,25 @@
 #include <linux/vmalloc.h>
 #include <linux/file.h>
 #include <linux/bitops.h>
+#include <linux/interrupt.h>
+#include <linux/spinlock.h>
+#include <linux/rcupdate.h>
+#include <linux/workqueue.h>
+
+struct fdtable_defer {
+       spinlock_t lock;
+       struct work_struct wq;
+       struct timer_list timer;
+       struct fdtable *next;
+};
+
+/*
+ * We use this list to defer free fdtables that have vmalloced
+ * sets/arrays. By keeping a per-cpu list, we avoid having to embed
+ * the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
+ * this per-task structure.
+ */
+static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
 
 
 /*
@@ -48,85 +67,143 @@ void free_fd_array(struct file **array, 
                vfree(array);
 }
 
-/*
- * Expand the fd array in the files_struct.  Called with the files
- * spinlock held for write.
- */
+static void __free_fdtable(struct fdtable *fdt)
+{
+       int fdset_size, fdarray_size;
 
-static int expand_fd_array(struct files_struct *files, int nr)
-       __releases(files->file_lock)
-       __acquires(files->file_lock)
+       fdset_size = fdt->max_fdset / 8;
+       fdarray_size = fdt->max_fds * sizeof(struct file *);
+       free_fdset(fdt->open_fds, fdset_size);
+       free_fdset(fdt->close_on_exec, fdset_size);
+       free_fd_array(fdt->fd, fdarray_size);
+       kfree(fdt);
+}
+
+static void fdtable_timer(unsigned long data)
 {
-       struct file **new_fds;
-       int error, nfds;
-       struct fdtable *fdt;
+       struct fdtable_defer *fddef = (struct fdtable_defer *)data;
 
-       
-       error = -EMFILE;
-       fdt = files_fdtable(files);
-       if (fdt->max_fds >= NR_OPEN || nr >= NR_OPEN)
+       spin_lock(&fddef->lock);
+       /*
+        * If someone already emptied the queue return.
+        */
+       if (!fddef->next)
                goto out;
+       if (!schedule_work(&fddef->wq))
+               mod_timer(&fddef->timer, 5);
+out:
+       spin_unlock(&fddef->lock);
+}
 
-       nfds = fdt->max_fds;
-       spin_unlock(&files->file_lock);
+static void free_fdtable_work(struct fdtable_defer *f)
+{
+       struct fdtable *fdt;
 
-       /* 
-        * Expand to the max in easy steps, and keep expanding it until
-        * we have enough for the requested fd array size. 
-        */
+       spin_lock_bh(&f->lock);
+       fdt = f->next;
+       f->next = NULL;
+       spin_unlock_bh(&f->lock);
+       while(fdt) {
+               struct fdtable *next = fdt->next;
+               __free_fdtable(fdt);
+               fdt = next;
+       }
+}
 
-       do {
-#if NR_OPEN_DEFAULT < 256
-               if (nfds < 256)
-                       nfds = 256;
-               else 
-#endif
-               if (nfds < (PAGE_SIZE / sizeof(struct file *)))
-                       nfds = PAGE_SIZE / sizeof(struct file *);
-               else {
-                       nfds = nfds * 2;
-                       if (nfds > NR_OPEN)
-                               nfds = NR_OPEN;
-               }
-       } while (nfds <= nr);
+static void free_fdtable_rcu(struct rcu_head *rcu)
+{
+       struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
+       int fdset_size, fdarray_size;
+       struct fdtable_defer *fddef;
+
+       BUG_ON(!fdt);
+       fdset_size = fdt->max_fdset / 8;
+       fdarray_size = fdt->max_fds * sizeof(struct file *);
+
+       if (fdt->free_files) {
+               /*
+                * The this fdtable was embedded in the files structure
+                * and the files structure itself was getting destroyed.
+                * It is now safe to free the files structure.
+                */
+               kmem_cache_free(files_cachep, fdt->free_files);
+               return;
+       }
+       if (fdt->max_fdset <= __FD_SETSIZE && fdt->max_fds <= NR_OPEN_DEFAULT) {
+               /*
+                * The fdtable was embedded
+                */
+               return;
+       }
+       if (fdset_size <= PAGE_SIZE && fdarray_size <= PAGE_SIZE) {
+               kfree(fdt->open_fds);
+               kfree(fdt->close_on_exec);
+               kfree(fdt->fd);
+               kfree(fdt);
+       } else {
+               fddef = &get_cpu_var(fdtable_defer_list);
+               spin_lock(&fddef->lock);
+               fdt->next = fddef->next;
+               fddef->next = fdt;
+               /*
+                * vmallocs are handled from the workqueue context.
+                * If the per-cpu workqueue is running, then we
+                * defer work scheduling through a timer.
+                */
+               if (!schedule_work(&fddef->wq))
+                       mod_timer(&fddef->timer, 5);
+               spin_unlock(&fddef->lock);
+               put_cpu_var(fdtable_defer_list);
+       }
+}
 
-       error = -ENOMEM;
-       new_fds = alloc_fd_array(nfds);
-       spin_lock(&files->file_lock);
-       if (!new_fds)
-               goto out;
+void free_fdtable(struct fdtable *fdt)
+{
+       if (fdt->free_files || fdt->max_fdset > __FD_SETSIZE ||
+                                       fdt->max_fds > NR_OPEN_DEFAULT)
+               call_rcu(&fdt->rcu, free_fdtable_rcu);
+}
 
-       /* Copy the existing array and install the new pointer */
-       fdt = files_fdtable(files);
+/*
+ * Expand the fdset in the files_struct.  Called with the files spinlock
+ * held for write.
+ */
+static void copy_fdtable(struct fdtable *nfdt, struct fdtable *fdt)
+{
+       int i;
+       int count;
 
-       if (nfds > fdt->max_fds) {
-               struct file **old_fds;
-               int i;
-               
-               old_fds = xchg(&fdt->fd, new_fds);
-               i = xchg(&fdt->max_fds, nfds);
-
-               /* Don't copy/clear the array if we are creating a new
-                  fd array for fork() */
-               if (i) {
-                       memcpy(new_fds, old_fds, i * sizeof(struct file *));
-                       /* clear the remainder of the array */
-                       memset(&new_fds[i], 0,
-                              (nfds-i) * sizeof(struct file *)); 
-
-                       spin_unlock(&files->file_lock);
-                       free_fd_array(old_fds, i);
-                       spin_lock(&files->file_lock);
-               }
-       } else {
-               /* Somebody expanded the array while we slept ... */
-               spin_unlock(&files->file_lock);
-               free_fd_array(new_fds, nfds);
-               spin_lock(&files->file_lock);
+       BUG_ON(nfdt->max_fdset < fdt->max_fdset);
+       BUG_ON(nfdt->max_fds < fdt->max_fds);
+       /* Copy the existing tables and install the new pointers */
+
+       i = fdt->max_fdset / (sizeof(unsigned long) * 8);
+       count = (nfdt->max_fdset - fdt->max_fdset) / 8;
+
+       /*
+        * Don't copy the entire array if the current fdset is
+        * not yet initialised.
+        */
+       if (i) {
+               memcpy (nfdt->open_fds, fdt->open_fds,
+                                               fdt->max_fdset/8);
+               memcpy (nfdt->close_on_exec, fdt->close_on_exec,
+                                               fdt->max_fdset/8);
+               memset (&nfdt->open_fds->fds_bits[i], 0, count);
+               memset (&nfdt->close_on_exec->fds_bits[i], 0, count);
        }
-       error = 0;
-out:
-       return error;
+
+       /* Don't copy/clear the array if we are creating a new
+          fd array for fork() */
+       if (fdt->max_fds) {
+               memcpy(nfdt->fd, fdt->fd,
+                       fdt->max_fds * sizeof(struct file *));
+               /* clear the remainder of the array */
+               memset(&nfdt->fd[fdt->max_fds], 0,
+                      (nfdt->max_fds - fdt->max_fds) *
+                                       sizeof(struct file *));
+       }
+       nfdt->next_fd = fdt->next_fd;
 }
 
 /*
@@ -157,28 +234,21 @@ void free_fdset(fd_set *array, int num)
                vfree(array);
 }
 
-/*
- * Expand the fdset in the files_struct.  Called with the files spinlock
- * held for write.
- */
-static int expand_fdset(struct files_struct *files, int nr)
-       __releases(file->file_lock)
-       __acquires(file->file_lock)
+static struct fdtable *alloc_fdtable(int nr)
 {
-       fd_set *new_openset = NULL, *new_execset = NULL;
-       int error, nfds = 0;
-       struct fdtable *fdt;
-
-       error = -EMFILE;
-       fdt = files_fdtable(files);
-       if (fdt->max_fdset >= NR_OPEN || nr >= NR_OPEN)
-               goto out;
-
-       nfds = fdt->max_fdset;
-       spin_unlock(&files->file_lock);
+       struct fdtable *fdt = NULL;
+       int nfds = 0;
+       fd_set *new_openset = NULL, *new_execset = NULL;
+       struct file **new_fds;
 
-       /* Expand to the max in easy steps */
-       do {
+       fdt = kmalloc(sizeof(*fdt), GFP_KERNEL);
+       if (!fdt)
+               goto out;
+       memset(fdt, 0, sizeof(*fdt));
+
+       nfds = __FD_SETSIZE;
+       /* Expand to the max in easy steps */
+       do {
                if (nfds < (PAGE_SIZE * 8))
                        nfds = PAGE_SIZE * 8;
                else {
@@ -188,50 +258,88 @@ static int expand_fdset(struct files_str
                }
        } while (nfds <= nr);
 
-       error = -ENOMEM;
-       new_openset = alloc_fdset(nfds);
-       new_execset = alloc_fdset(nfds);
-       spin_lock(&files->file_lock);
-       if (!new_openset || !new_execset)
+       new_openset = alloc_fdset(nfds);
+       new_execset = alloc_fdset(nfds);
+       if (!new_openset || !new_execset)
+               goto out;
+       fdt->open_fds = new_openset;
+       fdt->close_on_exec = new_execset;
+       fdt->max_fdset = nfds;
+
+       nfds = NR_OPEN_DEFAULT;
+       /*
+        * Expand to the max in easy steps, and keep expanding it until
+        * we have enough for the requested fd array size.
+        */
+       do {
+#if NR_OPEN_DEFAULT < 256
+               if (nfds < 256)
+                       nfds = 256;
+               else
+#endif
+               if (nfds < (PAGE_SIZE / sizeof(struct file *)))
+                       nfds = PAGE_SIZE / sizeof(struct file *);
+               else {
+                       nfds = nfds * 2;
+                       if (nfds > NR_OPEN)
+                               nfds = NR_OPEN;
+               }
+       } while (nfds <= nr);
+       new_fds = alloc_fd_array(nfds);
+       if (!new_fds)
                goto out;
+       fdt->fd = new_fds;
+       fdt->max_fds = nfds;
+       fdt->free_files = NULL;
+       return fdt;
+out:
+       if (new_openset)
+               free_fdset(new_openset, nfds);
+       if (new_execset)
+               free_fdset(new_execset, nfds);
+       kfree(fdt);
+       return NULL;
+}
 
-       error = 0;
-       
-       /* Copy the existing tables and install the new pointers */
+/*
+ * Expands the file descriptor table - it will allocate a new fdtable and
+ * both fd array and fdset. It is expected to be called with the
+ * files_lock held.
+ */
+static int expand_fdtable(struct files_struct *files, int nr)
+       __releases(files->file_lock)
+       __acquires(files->file_lock)
+{
+       int error = 0;
+       struct fdtable *fdt;
+       struct fdtable *nfdt = NULL;
+
+       spin_unlock(&files->file_lock);
+       nfdt = alloc_fdtable(nr);
+       if (!nfdt) {
+               error = -ENOMEM;
+               spin_lock(&files->file_lock);
+               goto out;
+       }
+
+       spin_lock(&files->file_lock);
        fdt = files_fdtable(files);
-       if (nfds > fdt->max_fdset) {
-               int i = fdt->max_fdset / (sizeof(unsigned long) * 8);
-               int count = (nfds - fdt->max_fdset) / 8;
-               
-               /* 
-                * Don't copy the entire array if the current fdset is
-                * not yet initialised.  
-                */
-               if (i) {
-                       memcpy (new_openset, fdt->open_fds, fdt->max_fdset/8);
-                       memcpy (new_execset, fdt->close_on_exec, 
fdt->max_fdset/8);
-                       memset (&new_openset->fds_bits[i], 0, count);
-                       memset (&new_execset->fds_bits[i], 0, count);
-               }
-               
-               nfds = xchg(&fdt->max_fdset, nfds);
-               new_openset = xchg(&fdt->open_fds, new_openset);
-               new_execset = xchg(&fdt->close_on_exec, new_execset);
+       /*
+        * Check again since another task may have expanded the
+        * fd table while we dropped the lock
+        */
+       if (nr >= fdt->max_fds || nr >= fdt->max_fdset) {
+               copy_fdtable(nfdt, fdt);
+       } else {
+               /* Somebody expanded while we dropped file_lock */
                spin_unlock(&files->file_lock);
-               free_fdset (new_openset, nfds);
-               free_fdset (new_execset, nfds);
+               __free_fdtable(nfdt);
                spin_lock(&files->file_lock);
-               return 0;
-       } 
-       /* Somebody expanded the array while we slept ... */
-
+               goto out;
+       }
+       rcu_assign_pointer(files->fdt, nfdt);
+       free_fdtable(fdt);
 out:
-       spin_unlock(&files->file_lock);
-       if (new_openset)
-               free_fdset(new_openset, nfds);
-       if (new_execset)
-               free_fdset(new_execset, nfds);
-       spin_lock(&files->file_lock);
        return error;
 }
 
@@ -246,17 +354,36 @@ int expand_files(struct files_struct *fi
        struct fdtable *fdt;
 
        fdt = files_fdtable(files);
-       if (nr >= fdt->max_fdset) {
-               expand = 1;
-               if ((err = expand_fdset(files, nr)))
+       if (nr >= fdt->max_fdset || nr >= fdt->max_fds) {
+               if (fdt->max_fdset >= NR_OPEN ||
+                       fdt->max_fds >= NR_OPEN || nr >= NR_OPEN) {
+                       err = -EMFILE;
                        goto out;
-       }
-       if (nr >= fdt->max_fds) {
+               }
                expand = 1;
-               if ((err = expand_fd_array(files, nr)))
+               if ((err = expand_fdtable(files, nr)))
                        goto out;
        }
        err = expand;
 out:
        return err;
 }
+
+static void __devinit fdtable_defer_list_init(int cpu)
+{
+       struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
+       spin_lock_init(&fddef->lock);
+       INIT_WORK(&fddef->wq, (void (*)(void *))free_fdtable_work, fddef);
+       init_timer(&fddef->timer);
+       fddef->timer.data = (unsigned long)fddef;
+       fddef->timer.function = fdtable_timer;
+       fddef->next = NULL;
+}
+
+void __init files_defer_init(void)
+{
+       int i;
+       /* Really early - can't use for_each_cpu */
+       for (i = 0; i < NR_CPUS; i++)
+               fdtable_defer_list_init(i);
+}
diff --git a/fs/file_table.c b/fs/file_table.c
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -14,6 +14,7 @@
 #include <linux/fs.h>
 #include <linux/security.h>
 #include <linux/eventpoll.h>
+#include <linux/rcupdate.h>
 #include <linux/mount.h>
 #include <linux/cdev.h>
 #include <linux/fsnotify.h>
@@ -53,11 +54,17 @@ void filp_dtor(void * objp, struct kmem_
        spin_unlock_irqrestore(&filp_count_lock, flags);
 }
 
-static inline void file_free(struct file *f)
+static inline void file_free_rcu(struct rcu_head *head)
 {
+       struct file *f =  container_of(head, struct file, f_rcuhead);
        kmem_cache_free(filp_cachep, f);
 }
 
+static inline void file_free(struct file *f)
+{
+       call_rcu(&f->f_rcuhead, file_free_rcu);
+}
+
 /* Find an unused file structure and return a pointer to it.
  * Returns NULL, if there are no more free file structures or
  * we run out of memory.
@@ -110,7 +117,7 @@ EXPORT_SYMBOL(get_empty_filp);
 
 void fastcall fput(struct file *file)
 {
-       if (atomic_dec_and_test(&file->f_count))
+       if (rcuref_dec_and_test(&file->f_count))
                __fput(file);
 }
 
@@ -156,11 +163,17 @@ struct file fastcall *fget(unsigned int 
        struct file *file;
        struct files_struct *files = current->files;
 
-       spin_lock(&files->file_lock);
+       rcu_read_lock();
        file = fcheck_files(files, fd);
-       if (file)
-               get_file(file);
-       spin_unlock(&files->file_lock);
+       if (file) {
+               if (!rcuref_inc_lf(&file->f_count)) {
+                       /* File object ref couldn't be taken */
+                       rcu_read_unlock();
+                       return NULL;
+               }
+       }
+       rcu_read_unlock();
+
        return file;
 }
 
@@ -182,21 +195,25 @@ struct file fastcall *fget_light(unsigne
        if (likely((atomic_read(&files->count) == 1))) {
                file = fcheck_files(files, fd);
        } else {
-               spin_lock(&files->file_lock);
+               rcu_read_lock();
                file = fcheck_files(files, fd);
                if (file) {
-                       get_file(file);
-                       *fput_needed = 1;
+                       if (rcuref_inc_lf(&file->f_count))
+                               *fput_needed = 1;
+                       else
+                               /* Didn't get the reference, someone's freed */
+                               file = NULL;
                }
-               spin_unlock(&files->file_lock);
+               rcu_read_unlock();
        }
+
        return file;
 }
 
 
 void put_filp(struct file *file)
 {
-       if (atomic_dec_and_test(&file->f_count)) {
+       if (rcuref_dec_and_test(&file->f_count)) {
                security_file_free(file);
                file_kill(file);
                file_free(file);
@@ -257,4 +274,5 @@ void __init files_init(unsigned long mem
        files_stat.max_files = n; 
        if (files_stat.max_files < NR_FILE)
                files_stat.max_files = NR_FILE;
+       files_defer_init();
 } 
diff --git a/fs/open.c b/fs/open.c
--- a/fs/open.c
+++ b/fs/open.c
@@ -24,6 +24,7 @@
 #include <linux/personality.h>
 #include <linux/pagemap.h>
 #include <linux/syscalls.h>
+#include <linux/rcupdate.h>
 
 #include <asm/unistd.h>
 
@@ -930,9 +931,8 @@ void fastcall fd_install(unsigned int fd
        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 f
        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);
diff --git a/include/linux/file.h b/include/linux/file.h
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -9,6 +9,7 @@
 #include <linux/posix_types.h>
 #include <linux/compiler.h>
 #include <linux/spinlock.h>
+#include <linux/rcupdate.h>
 
 /*
  * The default fd array needs to be at least BITS_PER_LONG,
@@ -23,6 +24,9 @@ struct fdtable {
        struct file ** fd;      /* current fd array */
        fd_set *close_on_exec;
        fd_set *open_fds;
+       struct rcu_head rcu;
+       struct files_struct *free_files;
+       struct fdtable *next;
 };
 
 /*
@@ -31,13 +35,14 @@ struct fdtable {
 struct files_struct {
         atomic_t count;
         spinlock_t file_lock;     /* Protects all the below members.  Nests 
inside tsk->alloc_lock */
+       struct fdtable *fdt;
        struct fdtable fdtab;
         fd_set close_on_exec_init;
         fd_set open_fds_init;
         struct file * fd_array[NR_OPEN_DEFAULT];
 };
 
-#define files_fdtable(files) (&(files)->fdtab)
+#define files_fdtable(files) (rcu_dereference((files)->fdt))
 
 extern void FASTCALL(__fput(struct file *));
 extern void FASTCALL(fput(struct file *));
@@ -65,6 +70,8 @@ extern fd_set *alloc_fdset(int);
 extern void free_fdset(fd_set *, int);
 
 extern int expand_files(struct files_struct *, int nr);
+extern void free_fdtable(struct fdtable *fdt);
+extern void __init files_defer_init(void);
 
 static inline struct file * fcheck_files(struct files_struct *files, unsigned 
int fd)
 {
@@ -72,7 +79,7 @@ static inline struct file * fcheck_files
        struct fdtable *fdt = files_fdtable(files);
 
        if (fd < fdt->max_fds)
-               file = fdt->fd[fd];
+               file = rcu_dereference(fdt->fd[fd]);
        return file;
 }
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -9,6 +9,7 @@
 #include <linux/config.h>
 #include <linux/limits.h>
 #include <linux/ioctl.h>
+#include <linux/rcuref.h>
 
 /*
  * It's silly to have NR_OPEN bigger than NR_FILE, but you can change
@@ -597,12 +598,13 @@ struct file {
        spinlock_t              f_ep_lock;
 #endif /* #ifdef CONFIG_EPOLL */
        struct address_space    *f_mapping;
+       struct rcu_head         f_rcuhead;
 };
 extern spinlock_t files_lock;
 #define file_list_lock() spin_lock(&files_lock);
 #define file_list_unlock() spin_unlock(&files_lock);
 
-#define get_file(x)    atomic_inc(&(x)->f_count)
+#define get_file(x)    rcuref_inc(&(x)->f_count)
 #define file_count(x)  atomic_read(&(x)->f_count)
 
 #define        MAX_NON_LFS     ((1UL<<31) - 1)
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -2,6 +2,7 @@
 #define _LINUX__INIT_TASK_H
 
 #include <linux/file.h>
+#include <linux/rcupdate.h>
 
 #define INIT_FDTABLE \
 {                                                      \
@@ -11,12 +12,16 @@
        .fd             = &init_files.fd_array[0],      \
        .close_on_exec  = &init_files.close_on_exec_init, \
        .open_fds       = &init_files.open_fds_init,    \
+       .rcu            = RCU_HEAD_INIT,                \
+       .free_files     = NULL,                         \
+       .next           = NULL,                         \
 }
 
 #define INIT_FILES \
 {                                                      \
        .count          = ATOMIC_INIT(1),               \
        .file_lock      = SPIN_LOCK_UNLOCKED,           \
+       .fdt            = &init_files.fdtab,            \
        .fdtab          = INIT_FDTABLE,                 \
        .close_on_exec_init = { { 0, } },               \
        .open_fds_init  = { { 0, } },                   \
diff --git a/kernel/exit.c b/kernel/exit.c
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -411,15 +411,16 @@ void fastcall put_files_struct(struct fi
                close_files(files);
                /*
                 * Free the fd and fdset arrays if we expanded them.
+                * If the fdtable was embedded, pass files for freeing
+                * at the end of the RCU grace period. Otherwise,
+                * you can free files immediately.
                 */
                fdt = files_fdtable(files);
-               if (fdt->fd != &files->fd_array[0])
-                       free_fd_array(fdt->fd, fdt->max_fds);
-               if (fdt->max_fdset > __FD_SETSIZE) {
-                       free_fdset(fdt->open_fds, fdt->max_fdset);
-                       free_fdset(fdt->close_on_exec, fdt->max_fdset);
-               }
-               kmem_cache_free(files_cachep, files);
+               if (fdt == &files->fdtab)
+                       fdt->free_files = files;
+               else
+                       kmem_cache_free(files_cachep, files);
+               free_fdtable(fdt);
        }
 }
 
diff --git a/kernel/fork.c b/kernel/fork.c
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -35,6 +35,7 @@
 #include <linux/syscalls.h>
 #include <linux/jiffies.h>
 #include <linux/futex.h>
+#include <linux/rcupdate.h>
 #include <linux/ptrace.h>
 #include <linux/mount.h>
 #include <linux/audit.h>
@@ -565,13 +566,12 @@ static inline int copy_fs(unsigned long 
        return 0;
 }
 
-static int count_open_files(struct files_struct *files, int size)
+static int count_open_files(struct fdtable *fdt)
 {
+       int size = fdt->max_fdset;
        int i;
-       struct fdtable *fdt;
 
        /* Find the last open fd */
-       fdt = files_fdtable(files);
        for (i = size/(8*sizeof(long)); i > 0; ) {
                if (fdt->open_fds->fds_bits[--i])
                        break;
@@ -592,13 +592,17 @@ static struct files_struct *alloc_files(
        atomic_set(&newf->count, 1);
 
        spin_lock_init(&newf->file_lock);
-       fdt = files_fdtable(newf);
+       fdt = &newf->fdtab;
        fdt->next_fd = 0;
        fdt->max_fds = NR_OPEN_DEFAULT;
        fdt->max_fdset = __FD_SETSIZE;
        fdt->close_on_exec = &newf->close_on_exec_init;
        fdt->open_fds = &newf->open_fds_init;
        fdt->fd = &newf->fd_array[0];
+       INIT_RCU_HEAD(&fdt->rcu);
+       fdt->free_files = NULL;
+       fdt->next = NULL;
+       rcu_assign_pointer(newf->fdt, fdt);
 out:
        return newf;
 }
@@ -637,7 +641,7 @@ static int copy_files(unsigned long clon
        old_fdt = files_fdtable(oldf);
        new_fdt = files_fdtable(newf);
        size = old_fdt->max_fdset;
-       open_files = count_open_files(oldf, old_fdt->max_fdset);
+       open_files = count_open_files(old_fdt);
        expand = 0;
 
        /*
@@ -661,7 +665,14 @@ static int copy_files(unsigned long clon
                spin_unlock(&newf->file_lock);
                if (error < 0)
                        goto out_release;
+               new_fdt = files_fdtable(newf);
+               /*
+                * Reacquire the oldf lock and a pointer to its fd table
+                * who knows it may have a new bigger fd table. We need
+                * the latest pointer.
+                */
                spin_lock(&oldf->file_lock);
+               old_fdt = files_fdtable(oldf);
        }
 
        old_fds = old_fdt->fd;
@@ -683,7 +694,7 @@ static int copy_files(unsigned long clon
                         */
                        FD_CLR(open_files - i, new_fdt->open_fds);
                }
-               *new_fds++ = f;
+               rcu_assign_pointer(*new_fds++, f);
        }
        spin_unlock(&oldf->file_lock);
 
-
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