proc: Implement /proc/thread-self to point at the directory of the current thread

/proc/thread-self is derived from /proc/self.  /proc/thread-self
points to the directory in proc containing information about the
current thread.

This funtionality has been missing for a long time, and is tricky to
implement in userspace as gettid() is not exported by glibc.  More
importantly this allows fixing defects in /proc/mounts and /proc/net
where in a threaded application today they wind up being empty files
when only the initial pthread has exited, causing problems for other
threads.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

diff --git a/fs/proc/Makefile b/fs/proc/Makefile
index 239493e..7151ea4 100644 (file)
--- a/fs/proc/Makefile
+++ b/fs/proc/Makefile
@@ -23,6 +23,7 @@ proc-y        += version.o
 proc-y += softirqs.o
 proc-y += namespaces.o
 proc-y += self.o
+proc-y += thread_self.o
 proc-$(CONFIG_PROC_SYSCTL)     += proc_sysctl.o
 proc-$(CONFIG_NET)             += proc_net.o
 proc-$(CONFIG_PROC_KCORE)      += kcore.o

diff --git a/fs/proc/base.c b/fs/proc/base.c
index ed34e40..0131156 100644 (file)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2847,7 +2847,7 @@ retry:
        return iter;
 }
 
-#define TGID_OFFSET (FIRST_PROCESS_ENTRY + 1)
+#define TGID_OFFSET (FIRST_PROCESS_ENTRY + 2)
 
 /* for the /proc/ directory itself, after non-process stuff has been done */
 int proc_pid_readdir(struct file *file, struct dir_context *ctx)
@@ -2859,14 +2859,19 @@ int proc_pid_readdir(struct file *file, struct dir_context *ctx)
        if (pos >= PID_MAX_LIMIT + TGID_OFFSET)
                return 0;
 
-       if (pos == TGID_OFFSET - 1) {
+       if (pos == TGID_OFFSET - 2) {
                struct inode *inode = ns->proc_self->d_inode;
                if (!dir_emit(ctx, "self", 4, inode->i_ino, DT_LNK))
                        return 0;
-               iter.tgid = 0;
-       } else {
-               iter.tgid = pos - TGID_OFFSET;
+               ctx->pos = pos = pos + 1;
+       }
+       if (pos == TGID_OFFSET - 1) {
+               struct inode *inode = ns->proc_thread_self->d_inode;
+               if (!dir_emit(ctx, "thread-self", 11, inode->i_ino, DT_LNK))
+                       return 0;
+               ctx->pos = pos = pos + 1;
        }
+       iter.tgid = pos - TGID_OFFSET;
        iter.task = NULL;
        for (iter = next_tgid(ns, iter);
             iter.task;

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 0adbc02..333080d 100644 (file)
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -442,6 +442,7 @@ struct inode *proc_get_inode(struct super_block *sb, struct proc_dir_entry *de)
 int proc_fill_super(struct super_block *s)
 {
        struct inode *root_inode;
+       int ret;
 
        s->s_flags |= MS_NODIRATIME | MS_NOSUID | MS_NOEXEC;
        s->s_blocksize = 1024;
@@ -463,5 +464,9 @@ int proc_fill_super(struct super_block *s)
                return -ENOMEM;
        }
 
-       return proc_setup_self(s);
+       ret = proc_setup_self(s);
+       if (ret) {
+               return ret;
+       }
+       return proc_setup_thread_self(s);
 }

diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index 3ab6d14..ee04619 100644 (file)
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -233,6 +233,12 @@ static inline int proc_net_init(void) { return 0; }
  */
 extern int proc_setup_self(struct super_block *);
 
+/*
+ * proc_thread_self.c
+ */
+extern int proc_setup_thread_self(struct super_block *);
+extern void proc_thread_self_init(void);
+
 /*
  * proc_sysctl.c
  */

diff --git a/fs/proc/root.c b/fs/proc/root.c
index 5dbadec..48f1c03 100644 (file)
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -149,6 +149,8 @@ static void proc_kill_sb(struct super_block *sb)
        ns = (struct pid_namespace *)sb->s_fs_info;
        if (ns->proc_self)
                dput(ns->proc_self);
+       if (ns->proc_thread_self)
+               dput(ns->proc_thread_self);
        kill_anon_super(sb);
        put_pid_ns(ns);
 }
@@ -170,6 +172,7 @@ void __init proc_root_init(void)
                return;
 
        proc_self_init();
+       proc_thread_self_init();
        proc_symlink("mounts", NULL, "self/mounts");
 
        proc_net_init();

diff --git a/fs/proc/thread_self.c b/fs/proc/thread_self.c
new file mode 100644 (file)
index 0000000..59075b5
--- /dev/null
+++ b/fs/proc/thread_self.c
@@ -0,0 +1,85 @@
+#include <linux/sched.h>
+#include <linux/namei.h>
+#include <linux/slab.h>
+#include <linux/pid_namespace.h>
+#include "internal.h"
+
+/*
+ * /proc/thread_self:
+ */
+static int proc_thread_self_readlink(struct dentry *dentry, char __user *buffer,
+                             int buflen)
+{
+       struct pid_namespace *ns = dentry->d_sb->s_fs_info;
+       pid_t tgid = task_tgid_nr_ns(current, ns);
+       pid_t pid = task_pid_nr_ns(current, ns);
+       char tmp[PROC_NUMBUF + 6 + PROC_NUMBUF];
+       if (!pid)
+               return -ENOENT;
+       sprintf(tmp, "%d/task/%d", tgid, pid);
+       return readlink_copy(buffer, buflen, tmp);
+}
+
+static void *proc_thread_self_follow_link(struct dentry *dentry, struct nameidata *nd)
+{
+       struct pid_namespace *ns = dentry->d_sb->s_fs_info;
+       pid_t tgid = task_tgid_nr_ns(current, ns);
+       pid_t pid = task_pid_nr_ns(current, ns);
+       char *name = ERR_PTR(-ENOENT);
+       if (pid) {
+               name = kmalloc(PROC_NUMBUF + 6 + PROC_NUMBUF, GFP_KERNEL);
+               if (!name)
+                       name = ERR_PTR(-ENOMEM);
+               else
+                       sprintf(name, "%d/task/%d", tgid, pid);
+       }
+       nd_set_link(nd, name);
+       return NULL;
+}
+
+static const struct inode_operations proc_thread_self_inode_operations = {
+       .readlink       = proc_thread_self_readlink,
+       .follow_link    = proc_thread_self_follow_link,
+       .put_link       = kfree_put_link,
+};
+
+static unsigned thread_self_inum;
+
+int proc_setup_thread_self(struct super_block *s)
+{
+       struct inode *root_inode = s->s_root->d_inode;
+       struct pid_namespace *ns = s->s_fs_info;
+       struct dentry *thread_self;
+
+       mutex_lock(&root_inode->i_mutex);
+       thread_self = d_alloc_name(s->s_root, "thread-self");
+       if (thread_self) {
+               struct inode *inode = new_inode_pseudo(s);
+               if (inode) {
+                       inode->i_ino = thread_self_inum;
+                       inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
+                       inode->i_mode = S_IFLNK | S_IRWXUGO;
+                       inode->i_uid = GLOBAL_ROOT_UID;
+                       inode->i_gid = GLOBAL_ROOT_GID;
+                       inode->i_op = &proc_thread_self_inode_operations;
+                       d_add(thread_self, inode);
+               } else {
+                       dput(thread_self);
+                       thread_self = ERR_PTR(-ENOMEM);
+               }
+       } else {
+               thread_self = ERR_PTR(-ENOMEM);
+       }
+       mutex_unlock(&root_inode->i_mutex);
+       if (IS_ERR(thread_self)) {
+               pr_err("proc_fill_super: can't allocate /proc/thread_self\n");
+               return PTR_ERR(thread_self);
+       }
+       ns->proc_thread_self = thread_self;
+       return 0;
+}
+
+void __init proc_thread_self_init(void)
+{
+       proc_alloc_inum(&thread_self_inum);
+}

diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 7246ef3..1997ffc 100644 (file)
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -33,6 +33,7 @@ struct pid_namespace {
 #ifdef CONFIG_PROC_FS
        struct vfsmount *proc_mnt;
        struct dentry *proc_self;
+       struct dentry *proc_thread_self;
 #endif
 #ifdef CONFIG_BSD_PROCESS_ACCT
        struct bsd_acct_struct *bacct;