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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.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Konstantin Khlebnikov 2012-01-05 13:06:11 +04:00 committed by Greg Kroah-Hartman
parent a4834c102f
commit e9aba5158a
2 changed files with 31 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

34
fs/devpts/inode.c
View File

@ -41,8 +41,9 @@
* Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
*/
static int pty_limit = NR_UNIX98_PTY_DEFAULT;
static int pty_reserve = NR_UNIX98_PTY_RESERVE;
static int pty_limit_min;
static int pty_limit_max = NR_UNIX98_PTY_MAX;
static int pty_limit_max = INT_MAX;
static int pty_count;
static struct ctl_table pty_table[] = {
@ -54,6 +55,14 @@ static struct ctl_table pty_table[] = {
.proc_handler = proc_dointvec_minmax,
.extra1 = &pty_limit_min,
.extra2 = &pty_limit_max,
}, {
.procname = "reserve",
.maxlen = sizeof(int),
.mode = 0644,
.data = &pty_reserve,
.proc_handler = proc_dointvec_minmax,
.extra1 = &pty_limit_min,
.extra2 = &pty_limit_max,
}, {
.procname = "nr",
.maxlen = sizeof(int),
@ -94,10 +103,11 @@ struct pts_mount_opts {
umode_t mode;
umode_t ptmxmode;
int newinstance;
int max;
};
enum {
Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance,
Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance, Opt_max,
Opt_err
};
@ -108,6 +118,7 @@ static const match_table_t tokens = {
#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
{Opt_ptmxmode, "ptmxmode=%o"},
{Opt_newinstance, "newinstance"},
{Opt_max, "max=%d"},
#endif
{Opt_err, NULL}
};
@ -154,6 +165,7 @@ static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
opts->gid = 0;
opts->mode = DEVPTS_DEFAULT_MODE;
opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
opts->max = NR_UNIX98_PTY_MAX;
/* newinstance makes sense only on initial mount */
if (op == PARSE_MOUNT)
@ -197,6 +209,12 @@ static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
if (op == PARSE_MOUNT)
opts->newinstance = 1;
break;
case Opt_max:
if (match_int(&args[0], &option) ||
option < 0 || option > NR_UNIX98_PTY_MAX)
return -EINVAL;
opts->max = option;
break;
#endif
default:
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)
seq_printf(seq, ",mode=%03o", opts->mode);
#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
if (opts->max < NR_UNIX98_PTY_MAX)
seq_printf(seq, ",max=%d", opts->max);
#endif
return 0;
@ -483,6 +503,12 @@ retry:
return -ENOMEM;
mutex_lock(&allocated_ptys_lock);
if (pty_count >= pty_limit -
(fsi->mount_opts.newinstance ? pty_reserve : 0)) {
mutex_unlock(&allocated_ptys_lock);
return -ENOSPC;
}
ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
if (ida_ret < 0) {
mutex_unlock(&allocated_ptys_lock);
@ -491,10 +517,10 @@ retry:
return -EIO;
}
if (index >= pty_limit) {
if (index >= fsi->mount_opts.max) {
ida_remove(&fsi->allocated_ptys, index);
mutex_unlock(&allocated_ptys_lock);
return -EIO;
return -ENOSPC;
}
pty_count++;
mutex_unlock(&allocated_ptys_lock);

1
include/linux/tty.h
View File

@ -52,6 +52,7 @@
* hardcoded at present.)
*/
#define NR_UNIX98_PTY_DEFAULT 4096 /* Default maximum for Unix98 ptys */
#define NR_UNIX98_PTY_RESERVE 1024 /* Default reserve for main devpts */
#define NR_UNIX98_PTY_MAX (1 << MINORBITS) /* Absolute limit */
/*