xref: /openbmc/linux/fs/file.c (revision d5cb9783536a41df9f9cba5b0a1d78047ed787f7)
1 /*
2  *  linux/fs/file.c
3  *
4  *  Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes
5  *
6  *  Manage the dynamic fd arrays in the process files_struct.
7  */
8 
9 #include <linux/fs.h>
10 #include <linux/mm.h>
11 #include <linux/time.h>
12 #include <linux/slab.h>
13 #include <linux/vmalloc.h>
14 #include <linux/file.h>
15 #include <linux/bitops.h>
16 #include <linux/interrupt.h>
17 #include <linux/spinlock.h>
18 #include <linux/rcupdate.h>
19 #include <linux/workqueue.h>
20 
21 struct fdtable_defer {
22 	spinlock_t lock;
23 	struct work_struct wq;
24 	struct timer_list timer;
25 	struct fdtable *next;
26 };
27 
28 /*
29  * We use this list to defer free fdtables that have vmalloced
30  * sets/arrays. By keeping a per-cpu list, we avoid having to embed
31  * the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
32  * this per-task structure.
33  */
34 static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
35 
36 
37 /*
38  * Allocate an fd array, using kmalloc or vmalloc.
39  * Note: the array isn't cleared at allocation time.
40  */
41 struct file ** alloc_fd_array(int num)
42 {
43 	struct file **new_fds;
44 	int size = num * sizeof(struct file *);
45 
46 	if (size <= PAGE_SIZE)
47 		new_fds = (struct file **) kmalloc(size, GFP_KERNEL);
48 	else
49 		new_fds = (struct file **) vmalloc(size);
50 	return new_fds;
51 }
52 
53 void free_fd_array(struct file **array, int num)
54 {
55 	int size = num * sizeof(struct file *);
56 
57 	if (!array) {
58 		printk (KERN_ERR "free_fd_array: array = 0 (num = %d)\n", num);
59 		return;
60 	}
61 
62 	if (num <= NR_OPEN_DEFAULT) /* Don't free the embedded fd array! */
63 		return;
64 	else if (size <= PAGE_SIZE)
65 		kfree(array);
66 	else
67 		vfree(array);
68 }
69 
70 static void __free_fdtable(struct fdtable *fdt)
71 {
72 	free_fdset(fdt->open_fds, fdt->max_fdset);
73 	free_fdset(fdt->close_on_exec, fdt->max_fdset);
74 	free_fd_array(fdt->fd, fdt->max_fds);
75 	kfree(fdt);
76 }
77 
78 static void fdtable_timer(unsigned long data)
79 {
80 	struct fdtable_defer *fddef = (struct fdtable_defer *)data;
81 
82 	spin_lock(&fddef->lock);
83 	/*
84 	 * If someone already emptied the queue return.
85 	 */
86 	if (!fddef->next)
87 		goto out;
88 	if (!schedule_work(&fddef->wq))
89 		mod_timer(&fddef->timer, 5);
90 out:
91 	spin_unlock(&fddef->lock);
92 }
93 
94 static void free_fdtable_work(struct fdtable_defer *f)
95 {
96 	struct fdtable *fdt;
97 
98 	spin_lock_bh(&f->lock);
99 	fdt = f->next;
100 	f->next = NULL;
101 	spin_unlock_bh(&f->lock);
102 	while(fdt) {
103 		struct fdtable *next = fdt->next;
104 		__free_fdtable(fdt);
105 		fdt = next;
106 	}
107 }
108 
109 static void free_fdtable_rcu(struct rcu_head *rcu)
110 {
111 	struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
112 	int fdset_size, fdarray_size;
113 	struct fdtable_defer *fddef;
114 
115 	BUG_ON(!fdt);
116 	fdset_size = fdt->max_fdset / 8;
117 	fdarray_size = fdt->max_fds * sizeof(struct file *);
118 
119 	if (fdt->free_files) {
120 		/*
121 		 * The this fdtable was embedded in the files structure
122 		 * and the files structure itself was getting destroyed.
123 		 * It is now safe to free the files structure.
124 		 */
125 		kmem_cache_free(files_cachep, fdt->free_files);
126 		return;
127 	}
128 	if (fdt->max_fdset <= __FD_SETSIZE && fdt->max_fds <= NR_OPEN_DEFAULT) {
129 		/*
130 		 * The fdtable was embedded
131 		 */
132 		return;
133 	}
134 	if (fdset_size <= PAGE_SIZE && fdarray_size <= PAGE_SIZE) {
135 		kfree(fdt->open_fds);
136 		kfree(fdt->close_on_exec);
137 		kfree(fdt->fd);
138 		kfree(fdt);
139 	} else {
140 		fddef = &get_cpu_var(fdtable_defer_list);
141 		spin_lock(&fddef->lock);
142 		fdt->next = fddef->next;
143 		fddef->next = fdt;
144 		/*
145 		 * vmallocs are handled from the workqueue context.
146 		 * If the per-cpu workqueue is running, then we
147 		 * defer work scheduling through a timer.
148 		 */
149 		if (!schedule_work(&fddef->wq))
150 			mod_timer(&fddef->timer, 5);
151 		spin_unlock(&fddef->lock);
152 		put_cpu_var(fdtable_defer_list);
153 	}
154 }
155 
156 void free_fdtable(struct fdtable *fdt)
157 {
158 	if (fdt->free_files || fdt->max_fdset > __FD_SETSIZE ||
159 					fdt->max_fds > NR_OPEN_DEFAULT)
160 		call_rcu(&fdt->rcu, free_fdtable_rcu);
161 }
162 
163 /*
164  * Expand the fdset in the files_struct.  Called with the files spinlock
165  * held for write.
166  */
167 static void copy_fdtable(struct fdtable *nfdt, struct fdtable *fdt)
168 {
169 	int i;
170 	int count;
171 
172 	BUG_ON(nfdt->max_fdset < fdt->max_fdset);
173 	BUG_ON(nfdt->max_fds < fdt->max_fds);
174 	/* Copy the existing tables and install the new pointers */
175 
176 	i = fdt->max_fdset / (sizeof(unsigned long) * 8);
177 	count = (nfdt->max_fdset - fdt->max_fdset) / 8;
178 
179 	/*
180 	 * Don't copy the entire array if the current fdset is
181 	 * not yet initialised.
182 	 */
183 	if (i) {
184 		memcpy (nfdt->open_fds, fdt->open_fds,
185 						fdt->max_fdset/8);
186 		memcpy (nfdt->close_on_exec, fdt->close_on_exec,
187 						fdt->max_fdset/8);
188 		memset (&nfdt->open_fds->fds_bits[i], 0, count);
189 		memset (&nfdt->close_on_exec->fds_bits[i], 0, count);
190 	}
191 
192 	/* Don't copy/clear the array if we are creating a new
193 	   fd array for fork() */
194 	if (fdt->max_fds) {
195 		memcpy(nfdt->fd, fdt->fd,
196 			fdt->max_fds * sizeof(struct file *));
197 		/* clear the remainder of the array */
198 		memset(&nfdt->fd[fdt->max_fds], 0,
199 		       (nfdt->max_fds - fdt->max_fds) *
200 					sizeof(struct file *));
201 	}
202 	nfdt->next_fd = fdt->next_fd;
203 }
204 
205 /*
206  * Allocate an fdset array, using kmalloc or vmalloc.
207  * Note: the array isn't cleared at allocation time.
208  */
209 fd_set * alloc_fdset(int num)
210 {
211 	fd_set *new_fdset;
212 	int size = num / 8;
213 
214 	if (size <= PAGE_SIZE)
215 		new_fdset = (fd_set *) kmalloc(size, GFP_KERNEL);
216 	else
217 		new_fdset = (fd_set *) vmalloc(size);
218 	return new_fdset;
219 }
220 
221 void free_fdset(fd_set *array, int num)
222 {
223 	int size = num / 8;
224 
225 	if (num <= __FD_SETSIZE) /* Don't free an embedded fdset */
226 		return;
227 	else if (size <= PAGE_SIZE)
228 		kfree(array);
229 	else
230 		vfree(array);
231 }
232 
233 static struct fdtable *alloc_fdtable(int nr)
234 {
235 	struct fdtable *fdt = NULL;
236 	int nfds = 0;
237   	fd_set *new_openset = NULL, *new_execset = NULL;
238 	struct file **new_fds;
239 
240 	fdt = kmalloc(sizeof(*fdt), GFP_KERNEL);
241 	if (!fdt)
242   		goto out;
243 	memset(fdt, 0, sizeof(*fdt));
244 
245 	nfds = __FD_SETSIZE;
246   	/* Expand to the max in easy steps */
247   	do {
248 		if (nfds < (PAGE_SIZE * 8))
249 			nfds = PAGE_SIZE * 8;
250 		else {
251 			nfds = nfds * 2;
252 			if (nfds > NR_OPEN)
253 				nfds = NR_OPEN;
254 		}
255 	} while (nfds <= nr);
256 
257   	new_openset = alloc_fdset(nfds);
258   	new_execset = alloc_fdset(nfds);
259   	if (!new_openset || !new_execset)
260   		goto out;
261 	fdt->open_fds = new_openset;
262 	fdt->close_on_exec = new_execset;
263 	fdt->max_fdset = nfds;
264 
265 	nfds = NR_OPEN_DEFAULT;
266 	/*
267 	 * Expand to the max in easy steps, and keep expanding it until
268 	 * we have enough for the requested fd array size.
269 	 */
270 	do {
271 #if NR_OPEN_DEFAULT < 256
272 		if (nfds < 256)
273 			nfds = 256;
274 		else
275 #endif
276 		if (nfds < (PAGE_SIZE / sizeof(struct file *)))
277 			nfds = PAGE_SIZE / sizeof(struct file *);
278 		else {
279 			nfds = nfds * 2;
280 			if (nfds > NR_OPEN)
281 				nfds = NR_OPEN;
282   		}
283 	} while (nfds <= nr);
284 	new_fds = alloc_fd_array(nfds);
285 	if (!new_fds)
286 		goto out;
287 	fdt->fd = new_fds;
288 	fdt->max_fds = nfds;
289 	fdt->free_files = NULL;
290 	return fdt;
291 out:
292   	if (new_openset)
293   		free_fdset(new_openset, nfds);
294   	if (new_execset)
295   		free_fdset(new_execset, nfds);
296 	kfree(fdt);
297 	return NULL;
298 }
299 
300 /*
301  * Expands the file descriptor table - it will allocate a new fdtable and
302  * both fd array and fdset. It is expected to be called with the
303  * files_lock held.
304  */
305 static int expand_fdtable(struct files_struct *files, int nr)
306 	__releases(files->file_lock)
307 	__acquires(files->file_lock)
308 {
309 	int error = 0;
310 	struct fdtable *fdt;
311 	struct fdtable *nfdt = NULL;
312 
313 	spin_unlock(&files->file_lock);
314 	nfdt = alloc_fdtable(nr);
315 	if (!nfdt) {
316 		error = -ENOMEM;
317 		spin_lock(&files->file_lock);
318 		goto out;
319 	}
320 
321 	spin_lock(&files->file_lock);
322 	fdt = files_fdtable(files);
323 	/*
324 	 * Check again since another task may have expanded the
325 	 * fd table while we dropped the lock
326 	 */
327 	if (nr >= fdt->max_fds || nr >= fdt->max_fdset) {
328 		copy_fdtable(nfdt, fdt);
329 	} else {
330 		/* Somebody expanded while we dropped file_lock */
331 		spin_unlock(&files->file_lock);
332 		__free_fdtable(nfdt);
333 		spin_lock(&files->file_lock);
334 		goto out;
335 	}
336 	rcu_assign_pointer(files->fdt, nfdt);
337 	free_fdtable(fdt);
338 out:
339 	return error;
340 }
341 
342 /*
343  * Expand files.
344  * Return <0 on error; 0 nothing done; 1 files expanded, we may have blocked.
345  * Should be called with the files->file_lock spinlock held for write.
346  */
347 int expand_files(struct files_struct *files, int nr)
348 {
349 	int err, expand = 0;
350 	struct fdtable *fdt;
351 
352 	fdt = files_fdtable(files);
353 	if (nr >= fdt->max_fdset || nr >= fdt->max_fds) {
354 		if (fdt->max_fdset >= NR_OPEN ||
355 			fdt->max_fds >= NR_OPEN || nr >= NR_OPEN) {
356 			err = -EMFILE;
357 			goto out;
358 		}
359 		expand = 1;
360 		if ((err = expand_fdtable(files, nr)))
361 			goto out;
362 	}
363 	err = expand;
364 out:
365 	return err;
366 }
367 
368 static void __devinit fdtable_defer_list_init(int cpu)
369 {
370 	struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
371 	spin_lock_init(&fddef->lock);
372 	INIT_WORK(&fddef->wq, (void (*)(void *))free_fdtable_work, fddef);
373 	init_timer(&fddef->timer);
374 	fddef->timer.data = (unsigned long)fddef;
375 	fddef->timer.function = fdtable_timer;
376 	fddef->next = NULL;
377 }
378 
379 void __init files_defer_init(void)
380 {
381 	int i;
382 	/* Really early - can't use for_each_cpu */
383 	for (i = 0; i < NR_CPUS; i++)
384 		fdtable_defer_list_init(i);
385 }
386