tty: rework pty count limiting

After adding devpts multiple-insrances sysctl kernel.pty.max limit pty count for each devpts instance independently, while kernel.pty.nr shows total pty count. This patch restores sysctl kernel.pty.max as global limit (4096 by default), adds pty reseve for main devpts (mounted without "newinstance" argument), and new sysctl to tune it: kernel.pty.reserve (1024 by default) Also it adds devpts mount option "max=%d" to limit pty count for each devpts instance independently. (by default NR_UNIX98_PTY_MAX == 2^20) Thus devpts instances in containers cannot eat up all available pty even if we didn't set any limits, while with "max" argument we can adjust limits more precisely. Plus, now open("/dev/ptmx") return -ENOSPC in case lack of pty indexes, this is more informative than -EIO.

Konstantin Khlebnikov committed 14 years ago

Commit e9aba511 parent a4834c12 files · +31 −4Browse files

Showing the changes to fs/devpts (1 of 2 files). Show all

Unified · Split

fs/devpts/inode.c+30−4

@@ -41,8 +41,9 @@ · 40 unmodified lines
41	41	* Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
42	42	*/
43	43	static int pty_limit = NR_UNIX98_PTY_DEFAULT;
	44	+static int pty_reserve = NR_UNIX98_PTY_RESERVE;
44	45	static int pty_limit_min;
45		−static int pty_limit_max = NR_UNIX98_PTY_MAX;
	46	+static int pty_limit_max = INT_MAX;
46	47	static int pty_count;
47	48
48	49	static struct ctl_table pty_table[] = {
@@ -54,6 +55,14 @@ static struct ctl_table pty_table[] = { · 5 unmodified lines
54	55	.proc_handler = proc_dointvec_minmax,
55	56	.extra1 = &pty_limit_min,
56	57	.extra2 = &pty_limit_max,
	58	+ }, {
	59	+ .procname = "reserve",
	60	+ .maxlen = sizeof(int),
	61	+ .mode = 0644,
	62	+ .data = &pty_reserve,
	63	+ .proc_handler = proc_dointvec_minmax,
	64	+ .extra1 = &pty_limit_min,
	65	+ .extra2 = &pty_limit_max,
57	66	}, {
58	67	.procname = "nr",
59	68	.maxlen = sizeof(int),
@@ -94,10 +103,11 @@ struct pts_mount_opts { · 34 unmodified lines
94	103	umode_t mode;
95	104	umode_t ptmxmode;
96	105	int newinstance;
	106	+ int max;
97	107	};
98	108
99	109	enum {
100		− Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance,
	110	+ Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance, Opt_max,
101	111	Opt_err
102	112	};
103	113
@@ -108,6 +118,7 @@ static const match_table_t tokens = { · 4 unmodified lines
108	118	#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
109	119	{Opt_ptmxmode, "ptmxmode=%o"},
110	120	{Opt_newinstance, "newinstance"},
	121	+ {Opt_max, "max=%d"},
111	122	#endif
112	123	{Opt_err, NULL}
113	124	};
@@ -154,6 +165,7 @@ static int parse_mount_options(char data, int op, struct pts_mount_opts opts) · 40 unmodified lines
154	165	opts->gid = 0;
155	166	opts->mode = DEVPTS_DEFAULT_MODE;
156	167	opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
	168	+ opts->max = NR_UNIX98_PTY_MAX;
157	169
158	170	/* newinstance makes sense only on initial mount */
159	171	if (op == PARSE_MOUNT)
@@ -197,6 +209,12 @@ static int parse_mount_options(char data, int op, struct pts_mount_opts opts) · 37 unmodified lines
197	209	if (op == PARSE_MOUNT)
198	210	opts->newinstance = 1;
199	211	break;
	212	+ case Opt_max:
	213	+ if (match_int(&args[0], &option) \|\|
	214	+ option < 0 \|\| option > NR_UNIX98_PTY_MAX)
	215	+ return -EINVAL;
	216	+ opts->max = option;
	217	+ break;
200	218	#endif
201	219	default:
202	220	printk(KERN_ERR "devpts: called with bogus options\n");
@@ -303,6 +321,8 @@ static int devpts_show_options(struct seq_file seq, struct dentry root) · 100 unmodified lines
303	321	seq_printf(seq, ",mode=%03o", opts->mode);
304	322	#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
305	323	seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
	324	+ if (opts->max < NR_UNIX98_PTY_MAX)
	325	+ seq_printf(seq, ",max=%d", opts->max);
306	326	#endif
307	327
308	328	return 0;
@@ -483,6 +503,12 @@ retry: · 174 unmodified lines
483	503	return -ENOMEM;
484	504
485	505	mutex_lock(&allocated_ptys_lock);
	506	+ if (pty_count >= pty_limit -
	507	+ (fsi->mount_opts.newinstance ? pty_reserve : 0)) {
	508	+ mutex_unlock(&allocated_ptys_lock);
	509	+ return -ENOSPC;
	510	+ }
	511	+
486	512	ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
487	513	if (ida_ret < 0) {
488	514	mutex_unlock(&allocated_ptys_lock);
@@ -491,10 +517,10 @@ retry: · 2 unmodified lines
491	517	return -EIO;
492	518	}
493	519
494		− if (index >= pty_limit) {
	520	+ if (index >= fsi->mount_opts.max) {
495	521	ida_remove(&fsi->allocated_ptys, index);
496	522	mutex_unlock(&allocated_ptys_lock);
497		− return -EIO;
	523	+ return -ENOSPC;
498	524	}
499	525	pty_count++;
500	526	mutex_unlock(&allocated_ptys_lock);