xref: /openbmc/linux/fs/file.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
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 fdtable *next;
25 };
26 
27 /*
28  * We use this list to defer free fdtables that have vmalloced
29  * sets/arrays. By keeping a per-cpu list, we avoid having to embed
30  * the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
31  * this per-task structure.
32  */
33 static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
34 
35 static inline void * alloc_fdmem(unsigned int size)
36 {
37 	if (size <= PAGE_SIZE)
38 		return kmalloc(size, GFP_KERNEL);
39 	else
40 		return vmalloc(size);
41 }
42 
43 static inline void free_fdarr(struct fdtable *fdt)
44 {
45 	if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *)))
46 		kfree(fdt->fd);
47 	else
48 		vfree(fdt->fd);
49 }
50 
51 static inline void free_fdset(struct fdtable *fdt)
52 {
53 	if (fdt->max_fds <= (PAGE_SIZE * BITS_PER_BYTE / 2))
54 		kfree(fdt->open_fds);
55 	else
56 		vfree(fdt->open_fds);
57 }
58 
59 static void free_fdtable_work(struct work_struct *work)
60 {
61 	struct fdtable_defer *f =
62 		container_of(work, struct fdtable_defer, wq);
63 	struct fdtable *fdt;
64 
65 	spin_lock_bh(&f->lock);
66 	fdt = f->next;
67 	f->next = NULL;
68 	spin_unlock_bh(&f->lock);
69 	while(fdt) {
70 		struct fdtable *next = fdt->next;
71 		vfree(fdt->fd);
72 		free_fdset(fdt);
73 		kfree(fdt);
74 		fdt = next;
75 	}
76 }
77 
78 void free_fdtable_rcu(struct rcu_head *rcu)
79 {
80 	struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
81 	struct fdtable_defer *fddef;
82 
83 	BUG_ON(!fdt);
84 
85 	if (fdt->max_fds <= NR_OPEN_DEFAULT) {
86 		/*
87 		 * This fdtable is embedded in the files structure and that
88 		 * structure itself is getting destroyed.
89 		 */
90 		kmem_cache_free(files_cachep,
91 				container_of(fdt, struct files_struct, fdtab));
92 		return;
93 	}
94 	if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *))) {
95 		kfree(fdt->fd);
96 		kfree(fdt->open_fds);
97 		kfree(fdt);
98 	} else {
99 		fddef = &get_cpu_var(fdtable_defer_list);
100 		spin_lock(&fddef->lock);
101 		fdt->next = fddef->next;
102 		fddef->next = fdt;
103 		/* vmallocs are handled from the workqueue context */
104 		schedule_work(&fddef->wq);
105 		spin_unlock(&fddef->lock);
106 		put_cpu_var(fdtable_defer_list);
107 	}
108 }
109 
110 /*
111  * Expand the fdset in the files_struct.  Called with the files spinlock
112  * held for write.
113  */
114 static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
115 {
116 	unsigned int cpy, set;
117 
118 	BUG_ON(nfdt->max_fds < ofdt->max_fds);
119 	if (ofdt->max_fds == 0)
120 		return;
121 
122 	cpy = ofdt->max_fds * sizeof(struct file *);
123 	set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *);
124 	memcpy(nfdt->fd, ofdt->fd, cpy);
125 	memset((char *)(nfdt->fd) + cpy, 0, set);
126 
127 	cpy = ofdt->max_fds / BITS_PER_BYTE;
128 	set = (nfdt->max_fds - ofdt->max_fds) / BITS_PER_BYTE;
129 	memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
130 	memset((char *)(nfdt->open_fds) + cpy, 0, set);
131 	memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy);
132 	memset((char *)(nfdt->close_on_exec) + cpy, 0, set);
133 }
134 
135 static struct fdtable * alloc_fdtable(unsigned int nr)
136 {
137 	struct fdtable *fdt;
138 	char *data;
139 
140 	/*
141 	 * Figure out how many fds we actually want to support in this fdtable.
142 	 * Allocation steps are keyed to the size of the fdarray, since it
143 	 * grows far faster than any of the other dynamic data. We try to fit
144 	 * the fdarray into comfortable page-tuned chunks: starting at 1024B
145 	 * and growing in powers of two from there on.
146 	 */
147 	nr /= (1024 / sizeof(struct file *));
148 	nr = roundup_pow_of_two(nr + 1);
149 	nr *= (1024 / sizeof(struct file *));
150 	if (nr > NR_OPEN)
151 		nr = NR_OPEN;
152 
153 	fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL);
154 	if (!fdt)
155 		goto out;
156 	fdt->max_fds = nr;
157 	data = alloc_fdmem(nr * sizeof(struct file *));
158 	if (!data)
159 		goto out_fdt;
160 	fdt->fd = (struct file **)data;
161 	data = alloc_fdmem(max_t(unsigned int,
162 				 2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
163 	if (!data)
164 		goto out_arr;
165 	fdt->open_fds = (fd_set *)data;
166 	data += nr / BITS_PER_BYTE;
167 	fdt->close_on_exec = (fd_set *)data;
168 	INIT_RCU_HEAD(&fdt->rcu);
169 	fdt->next = NULL;
170 
171 	return fdt;
172 
173 out_arr:
174 	free_fdarr(fdt);
175 out_fdt:
176 	kfree(fdt);
177 out:
178 	return NULL;
179 }
180 
181 /*
182  * Expand the file descriptor table.
183  * This function will allocate a new fdtable and both fd array and fdset, of
184  * the given size.
185  * Return <0 error code on error; 1 on successful completion.
186  * The files->file_lock should be held on entry, and will be held on exit.
187  */
188 static int expand_fdtable(struct files_struct *files, int nr)
189 	__releases(files->file_lock)
190 	__acquires(files->file_lock)
191 {
192 	struct fdtable *new_fdt, *cur_fdt;
193 
194 	spin_unlock(&files->file_lock);
195 	new_fdt = alloc_fdtable(nr);
196 	spin_lock(&files->file_lock);
197 	if (!new_fdt)
198 		return -ENOMEM;
199 	/*
200 	 * Check again since another task may have expanded the fd table while
201 	 * we dropped the lock
202 	 */
203 	cur_fdt = files_fdtable(files);
204 	if (nr >= cur_fdt->max_fds) {
205 		/* Continue as planned */
206 		copy_fdtable(new_fdt, cur_fdt);
207 		rcu_assign_pointer(files->fdt, new_fdt);
208 		if (cur_fdt->max_fds > NR_OPEN_DEFAULT)
209 			free_fdtable(cur_fdt);
210 	} else {
211 		/* Somebody else expanded, so undo our attempt */
212 		free_fdarr(new_fdt);
213 		free_fdset(new_fdt);
214 		kfree(new_fdt);
215 	}
216 	return 1;
217 }
218 
219 /*
220  * Expand files.
221  * This function will expand the file structures, if the requested size exceeds
222  * the current capacity and there is room for expansion.
223  * Return <0 error code on error; 0 when nothing done; 1 when files were
224  * expanded and execution may have blocked.
225  * The files->file_lock should be held on entry, and will be held on exit.
226  */
227 int expand_files(struct files_struct *files, int nr)
228 {
229 	struct fdtable *fdt;
230 
231 	fdt = files_fdtable(files);
232 	/* Do we need to expand? */
233 	if (nr < fdt->max_fds)
234 		return 0;
235 	/* Can we expand? */
236 	if (nr >= NR_OPEN)
237 		return -EMFILE;
238 
239 	/* All good, so we try */
240 	return expand_fdtable(files, nr);
241 }
242 
243 static void __devinit fdtable_defer_list_init(int cpu)
244 {
245 	struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
246 	spin_lock_init(&fddef->lock);
247 	INIT_WORK(&fddef->wq, free_fdtable_work);
248 	fddef->next = NULL;
249 }
250 
251 void __init files_defer_init(void)
252 {
253 	int i;
254 	for_each_possible_cpu(i)
255 		fdtable_defer_list_init(i);
256 }
257