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Message-Id: <20250424-work-pidfs-net-v1-3-0dc97227d854@kernel.org>
Date: Thu, 24 Apr 2025 14:24:36 +0200
From: Christian Brauner <brauner@...nel.org>
To: Oleg Nesterov <oleg@...hat.com>, Kuniyuki Iwashima <kuniyu@...zon.com>,
"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
Simon Horman <horms@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
netdev@...r.kernel.org, David Rheinsberg <david@...dahead.eu>,
Jan Kara <jack@...e.cz>, Alexander Mikhalitsyn <alexander@...alicyn.com>,
Luca Boccassi <bluca@...ian.org>,
Lennart Poettering <lennart@...ttering.net>,
Daan De Meyer <daan.j.demeyer@...il.com>, Mike Yuan <me@...dnzj.com>,
Christian Brauner <brauner@...nel.org>
Subject: [PATCH RFC 3/4] pidfs: get rid of __pidfd_prepare()
Fold it into pidfd_prepare() and rename PIDFD_CLONE to PIDFD_STALE to
indicate that the passed pid might not have task linkage and no explicit
check for that should be performed.
Signed-off-by: Christian Brauner <brauner@...nel.org>
---
fs/pidfs.c | 12 +++----
include/uapi/linux/pidfd.h | 2 +-
kernel/fork.c | 78 ++++++++++++++--------------------------------
3 files changed, 31 insertions(+), 61 deletions(-)
diff --git a/fs/pidfs.c b/fs/pidfs.c
index 8e6c11774c60..3199ec02aaec 100644
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -768,7 +768,7 @@ static inline bool pidfs_pid_valid(struct pid *pid, const struct path *path,
{
enum pid_type type;
- if (flags & PIDFD_CLONE)
+ if (flags & PIDFD_STALE)
return true;
/*
@@ -777,7 +777,7 @@ static inline bool pidfs_pid_valid(struct pid *pid, const struct path *path,
* pidfd has been allocated perform another check that the pid
* is still alive. If it is exit information is available even
* if the task gets reaped before the pidfd is returned to
- * userspace. The only exception is PIDFD_CLONE where no task
+ * userspace. The only exception is PIDFD_STALE where no task
* linkage has been established for @pid yet and the kernel is
* in the middle of process creation so there's nothing for
* pidfs to miss.
@@ -874,11 +874,11 @@ struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags)
int ret;
/*
- * Ensure that PIDFD_CLONE can be passed as a flag without
+ * Ensure that PIDFD_STALE can be passed as a flag without
* overloading other uapi pidfd flags.
*/
- BUILD_BUG_ON(PIDFD_CLONE == PIDFD_THREAD);
- BUILD_BUG_ON(PIDFD_CLONE == PIDFD_NONBLOCK);
+ BUILD_BUG_ON(PIDFD_STALE == PIDFD_THREAD);
+ BUILD_BUG_ON(PIDFD_STALE == PIDFD_NONBLOCK);
ret = path_from_stashed(&pid->stashed, pidfs_mnt, get_pid(pid), &path);
if (ret < 0)
@@ -887,7 +887,7 @@ struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags)
if (!pidfs_pid_valid(pid, &path, flags))
return ERR_PTR(-ESRCH);
- flags &= ~PIDFD_CLONE;
+ flags &= ~PIDFD_STALE;
pidfd_file = dentry_open(&path, flags, current_cred());
/* Raise PIDFD_THREAD explicitly as do_dentry_open() strips it. */
if (!IS_ERR(pidfd_file))
diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h
index 2970ef44655a..8c1511edd0e9 100644
--- a/include/uapi/linux/pidfd.h
+++ b/include/uapi/linux/pidfd.h
@@ -12,7 +12,7 @@
#define PIDFD_THREAD O_EXCL
#ifdef __KERNEL__
#include <linux/sched.h>
-#define PIDFD_CLONE CLONE_PIDFD
+#define PIDFD_STALE CLONE_PIDFD
#endif
/* Flags for pidfd_send_signal(). */
diff --git a/kernel/fork.c b/kernel/fork.c
index f7403e1fb0d4..365687e1698f 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2035,50 +2035,6 @@ static inline void rcu_copy_process(struct task_struct *p)
#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
}
-/**
- * __pidfd_prepare - allocate a new pidfd_file and reserve a pidfd
- * @pid: the struct pid for which to create a pidfd
- * @flags: flags of the new @pidfd
- * @ret: Where to return the file for the pidfd.
- *
- * Allocate a new file that stashes @pid and reserve a new pidfd number in the
- * caller's file descriptor table. The pidfd is reserved but not installed yet.
- *
- * The helper doesn't perform checks on @pid which makes it useful for pidfds
- * created via CLONE_PIDFD where @pid has no task attached when the pidfd and
- * pidfd file are prepared.
- *
- * If this function returns successfully the caller is responsible to either
- * call fd_install() passing the returned pidfd and pidfd file as arguments in
- * order to install the pidfd into its file descriptor table or they must use
- * put_unused_fd() and fput() on the returned pidfd and pidfd file
- * respectively.
- *
- * This function is useful when a pidfd must already be reserved but there
- * might still be points of failure afterwards and the caller wants to ensure
- * that no pidfd is leaked into its file descriptor table.
- *
- * Return: On success, a reserved pidfd is returned from the function and a new
- * pidfd file is returned in the last argument to the function. On
- * error, a negative error code is returned from the function and the
- * last argument remains unchanged.
- */
-static int __pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret)
-{
- struct file *pidfd_file;
-
- CLASS(get_unused_fd, pidfd)(O_CLOEXEC);
- if (pidfd < 0)
- return pidfd;
-
- pidfd_file = pidfs_alloc_file(pid, flags | O_RDWR);
- if (IS_ERR(pidfd_file))
- return PTR_ERR(pidfd_file);
-
- *ret = pidfd_file;
- return take_fd(pidfd);
-}
-
/**
* pidfd_prepare - allocate a new pidfd_file and reserve a pidfd
* @pid: the struct pid for which to create a pidfd
@@ -2108,14 +2064,19 @@ static int __pidfd_prepare(struct pid *pid, unsigned int flags, struct file **re
*/
int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret)
{
- /*
- * While holding the pidfd waitqueue lock removing the task
- * linkage for the thread-group leader pid (PIDTYPE_TGID) isn't
- * possible. Thus, if there's still task linkage for PIDTYPE_PID
- * not having thread-group leader linkage for the pid means it
- * wasn't a thread-group leader in the first place.
- */
- scoped_guard(spinlock_irq, &pid->wait_pidfd.lock) {
+ struct file *pidfd_file;
+
+ if (!(flags & PIDFD_STALE)) {
+ /*
+ * While holding the pidfd waitqueue lock removing the
+ * task linkage for the thread-group leader pid
+ * (PIDTYPE_TGID) isn't possible. Thus, if there's still
+ * task linkage for PIDTYPE_PID not having thread-group
+ * leader linkage for the pid means it wasn't a
+ * thread-group leader in the first place.
+ */
+ guard(spinlock_irq)(&pid->wait_pidfd.lock);
+
/* Task has already been reaped. */
if (!pid_has_task(pid, PIDTYPE_PID))
return -ESRCH;
@@ -2128,7 +2089,16 @@ int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret)
return -ENOENT;
}
- return __pidfd_prepare(pid, flags, ret);
+ CLASS(get_unused_fd, pidfd)(O_CLOEXEC);
+ if (pidfd < 0)
+ return pidfd;
+
+ pidfd_file = pidfs_alloc_file(pid, flags | O_RDWR);
+ if (IS_ERR(pidfd_file))
+ return PTR_ERR(pidfd_file);
+
+ *ret = pidfd_file;
+ return take_fd(pidfd);
}
static void __delayed_free_task(struct rcu_head *rhp)
@@ -2477,7 +2447,7 @@ __latent_entropy struct task_struct *copy_process(
* Note that no task has been attached to @pid yet indicate
* that via CLONE_PIDFD.
*/
- retval = __pidfd_prepare(pid, flags | PIDFD_CLONE, &pidfile);
+ retval = pidfd_prepare(pid, flags | PIDFD_STALE, &pidfile);
if (retval < 0)
goto bad_fork_free_pid;
pidfd = retval;
--
2.47.2
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