From e9aba5158a80098447ff207a452a3418ae7ee386 Mon Sep 17 00:00:00 2001 From: Konstantin Khlebnikov Date: Thu, 5 Jan 2012 13:06:11 +0400 Subject: [PATCH] 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 Signed-off-by: Greg Kroah-Hartman --- fs/devpts/inode.c | 34 ++++++++++++++++++++++++++++++---- include/linux/tty.h | 1 + 2 files changed, 31 insertions(+), 4 deletions(-) diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c index c2c7317d5687..1c6f908e38ca 100644 --- a/fs/devpts/inode.c +++ b/fs/devpts/inode.c @@ -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); diff --git a/include/linux/tty.h b/include/linux/tty.h index d3ebd765b548..d40774188203 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -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 */ /* -- 2.20.1