From: Dipankar Sarma 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 --- 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 -puN fs/aio.c~files-files-struct-with-rcu fs/aio.c --- 25/fs/aio.c~files-files-struct-with-rcu 2005-06-28 23:04:58.000000000 -0700 +++ 25-akpm/fs/aio.c 2005-06-28 23:04:58.000000000 -0700 @@ -29,6 +29,7 @@ #include #include #include +#include #include #include @@ -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 -puN fs/fcntl.c~files-files-struct-with-rcu fs/fcntl.c --- 25/fs/fcntl.c~files-files-struct-with-rcu 2005-06-28 23:04:58.000000000 -0700 +++ 25-akpm/fs/fcntl.c 2005-06-28 23:04:58.000000000 -0700 @@ -16,6 +16,7 @@ #include #include #include +#include #include #include @@ -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 -puN fs/file.c~files-files-struct-with-rcu fs/file.c --- 25/fs/file.c~files-files-struct-with-rcu 2005-06-28 23:04:58.000000000 -0700 +++ 25-akpm/fs/file.c 2005-06-28 23:04:58.000000000 -0700 @@ -13,6 +13,25 @@ #include #include #include +#include +#include +#include +#include + +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 -puN fs/file_table.c~files-files-struct-with-rcu fs/file_table.c --- 25/fs/file_table.c~files-files-struct-with-rcu 2005-06-28 23:04:58.000000000 -0700 +++ 25-akpm/fs/file_table.c 2005-06-28 23:04:58.000000000 -0700 @@ -14,6 +14,7 @@ #include #include #include +#include #include #include #include @@ -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. @@ -111,7 +118,7 @@ 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); } @@ -157,11 +164,17 @@ 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; } @@ -183,21 +196,25 @@ 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); @@ -258,4 +275,5 @@ 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-files-struct-with-rcu fs/open.c --- 25/fs/open.c~files-files-struct-with-rcu 2005-06-28 23:04:58.000000000 -0700 +++ 25-akpm/fs/open.c 2005-06-28 23:05:06.000000000 -0700 @@ -24,6 +24,7 @@ #include #include #include +#include #include @@ -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); } @@ -1021,7 +1021,7 @@ 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-files-struct-with-rcu include/linux/file.h --- 25/include/linux/file.h~files-files-struct-with-rcu 2005-06-28 23:04:58.000000000 -0700 +++ 25-akpm/include/linux/file.h 2005-06-28 23:04:58.000000000 -0700 @@ -9,6 +9,7 @@ #include #include #include +#include /* * 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-files-struct-with-rcu include/linux/fs.h --- 25/include/linux/fs.h~files-files-struct-with-rcu 2005-06-28 23:04:58.000000000 -0700 +++ 25-akpm/include/linux/fs.h 2005-06-28 23:04:58.000000000 -0700 @@ -9,6 +9,7 @@ #include #include #include +#include /* * It's silly to have NR_OPEN bigger than NR_FILE, but you can change @@ -607,12 +608,13 @@ 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-files-struct-with-rcu include/linux/init_task.h --- 25/include/linux/init_task.h~files-files-struct-with-rcu 2005-06-28 23:04:58.000000000 -0700 +++ 25-akpm/include/linux/init_task.h 2005-06-28 23:04:58.000000000 -0700 @@ -2,6 +2,7 @@ #define _LINUX__INIT_TASK_H #include +#include #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-files-struct-with-rcu kernel/exit.c --- 25/kernel/exit.c~files-files-struct-with-rcu 2005-06-28 23:04:58.000000000 -0700 +++ 25-akpm/kernel/exit.c 2005-06-28 23:04:58.000000000 -0700 @@ -413,15 +413,16 @@ 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-files-struct-with-rcu kernel/fork.c --- 25/kernel/fork.c~files-files-struct-with-rcu 2005-06-28 23:04:58.000000000 -0700 +++ 25-akpm/kernel/fork.c 2005-06-28 23:04:58.000000000 -0700 @@ -35,6 +35,7 @@ #include #include #include +#include #include #include #include @@ -563,13 +564,12 @@ 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; @@ -590,13 +590,17 @@ 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; } @@ -635,7 +639,7 @@ 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; /* @@ -659,7 +663,14 @@ 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; @@ -681,7 +692,7 @@ 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); _