Re: [PATCH 4/6] files: files struct with RCU

From: Dipankar Sarma
Date: Tue Jun 14 2005 - 09:40:03 EST




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.

This patch needs the rcuref api additions as pre-req.

Signed-off-by: Dipankar Sarma <dipankar@xxxxxxxxxx>


fs/aio.c | 3
fs/fcntl.c | 13 +
fs/file.c | 393 ++++++++++++++++++++++++++++++----------------
fs/file_table.c | 40 +++-
fs/open.c | 5
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(+), 166 deletions(-)

diff -puN fs/aio.c~files-struct-rcu fs/aio.c
--- linux-2.6.12-rc6-fd/fs/aio.c~files-struct-rcu 2005-06-14 14:05:05.000000000 +0530
+++ linux-2.6.12-rc6-fd-dipankar/fs/aio.c 2005-06-14 14:05:05.000000000 +0530
@@ -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>
@@ -498,7 +499,7 @@ 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 -puN fs/fcntl.c~files-struct-rcu fs/fcntl.c
--- linux-2.6.12-rc6-fd/fs/fcntl.c~files-struct-rcu 2005-06-14 14:05:05.000000000 +0530
+++ linux-2.6.12-rc6-fd-dipankar/fs/fcntl.c 2005-06-14 14:05:05.000000000 +0530
@@ -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:
@@ -162,7 +169,7 @@ 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 -puN fs/file.c~files-struct-rcu fs/file.c
--- linux-2.6.12-rc6-fd/fs/file.c~files-struct-rcu 2005-06-14 14:05:05.000000000 +0530
+++ linux-2.6.12-rc6-fd-dipankar/fs/file.c 2005-06-14 14:05:05.000000000 +0530
@@ -13,7 +13,26 @@
#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);
+

/*
* Allocate an fd array, using kmalloc or vmalloc.
@@ -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);
-
- /* Expand to the max in easy steps */
- do {
+ struct fdtable *fdt = NULL;
+ int nfds = 0;
+ fd_set *new_openset = NULL, *new_execset = NULL;
+ struct file **new_fds;
+
+ 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 -puN fs/file_table.c~files-struct-rcu fs/file_table.c
--- linux-2.6.12-rc6-fd/fs/file_table.c~files-struct-rcu 2005-06-14 14:05:05.000000000 +0530
+++ linux-2.6.12-rc6-fd-dipankar/fs/file_table.c 2005-06-14 14:05:05.000000000 +0530
@@ -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>

@@ -52,11 +53,17 @@ 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.
@@ -107,7 +114,7 @@ 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);
}

@@ -151,11 +158,17 @@ 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;
}

@@ -177,21 +190,25 @@ 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);
@@ -252,4 +269,5 @@ 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 -puN fs/open.c~files-struct-rcu fs/open.c
--- linux-2.6.12-rc6-fd/fs/open.c~files-struct-rcu 2005-06-14 14:05:05.000000000 +0530
+++ linux-2.6.12-rc6-fd-dipankar/fs/open.c 2005-06-14 14:05:05.000000000 +0530
@@ -23,6 +23,7 @@
#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/syscalls.h>
+#include <linux/rcupdate.h>

#include <asm/unistd.h>

@@ -929,7 +930,7 @@ void fastcall fd_install(unsigned int fd
fdt = files_fdtable(files);
if (unlikely(fdt->fd[fd] != NULL))
BUG();
- fdt->fd[fd] = file;
+ rcu_assign_pointer(fdt->fd[fd], file);
spin_unlock(&files->file_lock);
}

@@ -1029,7 +1030,7 @@ 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 -puN include/linux/file.h~files-struct-rcu include/linux/file.h
--- linux-2.6.12-rc6-fd/include/linux/file.h~files-struct-rcu 2005-06-14 14:05:05.000000000 +0530
+++ linux-2.6.12-rc6-fd-dipankar/include/linux/file.h 2005-06-14 14:05:05.000000000 +0530
@@ -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 -puN include/linux/fs.h~files-struct-rcu include/linux/fs.h
--- linux-2.6.12-rc6-fd/include/linux/fs.h~files-struct-rcu 2005-06-14 14:05:05.000000000 +0530
+++ linux-2.6.12-rc6-fd-dipankar/include/linux/fs.h 2005-06-14 14:05:05.000000000 +0530
@@ -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
@@ -600,12 +601,13 @@ 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 -puN include/linux/init_task.h~files-struct-rcu include/linux/init_task.h
--- linux-2.6.12-rc6-fd/include/linux/init_task.h~files-struct-rcu 2005-06-14 14:05:05.000000000 +0530
+++ linux-2.6.12-rc6-fd-dipankar/include/linux/init_task.h 2005-06-14 14:05:05.000000000 +0530
@@ -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 -puN kernel/exit.c~files-struct-rcu kernel/exit.c
--- linux-2.6.12-rc6-fd/kernel/exit.c~files-struct-rcu 2005-06-14 14:05:05.000000000 +0530
+++ linux-2.6.12-rc6-fd-dipankar/kernel/exit.c 2005-06-14 14:05:05.000000000 +0530
@@ -406,15 +406,16 @@ 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 -puN kernel/fork.c~files-struct-rcu kernel/fork.c
--- linux-2.6.12-rc6-fd/kernel/fork.c~files-struct-rcu 2005-06-14 14:05:05.000000000 +0530
+++ linux-2.6.12-rc6-fd-dipankar/kernel/fork.c 2005-06-14 14:05:05.000000000 +0530
@@ -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>
@@ -559,13 +560,12 @@ 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;
@@ -586,13 +586,17 @@ 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;
}
@@ -631,7 +635,7 @@ 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;

/*
@@ -655,7 +659,14 @@ 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;
@@ -677,7 +688,7 @@ 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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