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authorLinus Torvalds <torvalds@linux-foundation.org>2019-07-10 22:17:21 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2019-07-10 22:17:21 -0700
commit5450e8a316a64cddcbc15f90733ebc78aa736545 (patch)
tree176eefe81164b86efb8ab2d0dbdea5723d4c06d3 /kernel/pid.c
parent29cd581b59496c26334c910a8b848baa81a6becd (diff)
parent172bb24a4f480c180bee646f6616f714ac4bcab2 (diff)
Merge tag 'pidfd-updates-v5.3' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux
Pull pidfd updates from Christian Brauner: "This adds two main features. - First, it adds polling support for pidfds. This allows process managers to know when a (non-parent) process dies in a race-free way. The notification mechanism used follows the same logic that is currently used when the parent of a task is notified of a child's death. With this patchset it is possible to put pidfds in an {e}poll loop and get reliable notifications for process (i.e. thread-group) exit. - The second feature compliments the first one by making it possible to retrieve pollable pidfds for processes that were not created using CLONE_PIDFD. A lot of processes get created with traditional PID-based calls such as fork() or clone() (without CLONE_PIDFD). For these processes a caller can currently not create a pollable pidfd. This is a problem for Android's low memory killer (LMK) and service managers such as systemd. Both patchsets are accompanied by selftests. It's perhaps worth noting that the work done so far and the work done in this branch for pidfd_open() and polling support do already see some adoption: - Android is in the process of backporting this work to all their LTS kernels [1] - Service managers make use of pidfd_send_signal but will need to wait until we enable waiting on pidfds for full adoption. - And projects I maintain make use of both pidfd_send_signal and CLONE_PIDFD [2] and will use polling support and pidfd_open() too" [1] https://android-review.googlesource.com/q/topic:%22pidfd+polling+support+4.9+backport%22 https://android-review.googlesource.com/q/topic:%22pidfd+polling+support+4.14+backport%22 https://android-review.googlesource.com/q/topic:%22pidfd+polling+support+4.19+backport%22 [2] https://github.com/lxc/lxc/blob/aab6e3eb73c343231cdde775db938994fc6f2803/src/lxc/start.c#L1753 * tag 'pidfd-updates-v5.3' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux: tests: add pidfd_open() tests arch: wire-up pidfd_open() pid: add pidfd_open() pidfd: add polling selftests pidfd: add polling support
Diffstat (limited to 'kernel/pid.c')
-rw-r--r--kernel/pid.c71
1 files changed, 71 insertions, 0 deletions
diff --git a/kernel/pid.c b/kernel/pid.c
index e5cad0c7d5dd..16263b526560 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -38,6 +38,8 @@
#include <linux/syscalls.h>
#include <linux/proc_ns.h>
#include <linux/proc_fs.h>
+#include <linux/anon_inodes.h>
+#include <linux/sched/signal.h>
#include <linux/sched/task.h>
#include <linux/idr.h>
@@ -214,6 +216,8 @@ struct pid *alloc_pid(struct pid_namespace *ns)
for (type = 0; type < PIDTYPE_MAX; ++type)
INIT_HLIST_HEAD(&pid->tasks[type]);
+ init_waitqueue_head(&pid->wait_pidfd);
+
upid = pid->numbers + ns->level;
spin_lock_irq(&pidmap_lock);
if (!(ns->pid_allocated & PIDNS_ADDING))
@@ -451,6 +455,73 @@ struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
return idr_get_next(&ns->idr, &nr);
}
+/**
+ * pidfd_create() - Create a new pid file descriptor.
+ *
+ * @pid: struct pid that the pidfd will reference
+ *
+ * This creates a new pid file descriptor with the O_CLOEXEC flag set.
+ *
+ * Note, that this function can only be called after the fd table has
+ * been unshared to avoid leaking the pidfd to the new process.
+ *
+ * Return: On success, a cloexec pidfd is returned.
+ * On error, a negative errno number will be returned.
+ */
+static int pidfd_create(struct pid *pid)
+{
+ int fd;
+
+ fd = anon_inode_getfd("[pidfd]", &pidfd_fops, get_pid(pid),
+ O_RDWR | O_CLOEXEC);
+ if (fd < 0)
+ put_pid(pid);
+
+ return fd;
+}
+
+/**
+ * pidfd_open() - Open new pid file descriptor.
+ *
+ * @pid: pid for which to retrieve a pidfd
+ * @flags: flags to pass
+ *
+ * This creates a new pid file descriptor with the O_CLOEXEC flag set for
+ * the process identified by @pid. Currently, the process identified by
+ * @pid must be a thread-group leader. This restriction currently exists
+ * for all aspects of pidfds including pidfd creation (CLONE_PIDFD cannot
+ * be used with CLONE_THREAD) and pidfd polling (only supports thread group
+ * leaders).
+ *
+ * Return: On success, a cloexec pidfd is returned.
+ * On error, a negative errno number will be returned.
+ */
+SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags)
+{
+ int fd, ret;
+ struct pid *p;
+
+ if (flags)
+ return -EINVAL;
+
+ if (pid <= 0)
+ return -EINVAL;
+
+ p = find_get_pid(pid);
+ if (!p)
+ return -ESRCH;
+
+ ret = 0;
+ rcu_read_lock();
+ if (!pid_task(p, PIDTYPE_TGID))
+ ret = -EINVAL;
+ rcu_read_unlock();
+
+ fd = ret ?: pidfd_create(p);
+ put_pid(p);
+ return fd;
+}
+
void __init pid_idr_init(void)
{
/* Verify no one has done anything silly: */