[Lse-tech] [patch - RFC] simple task notifier support

[Jes S. <je...@sg...>]

Hi,

Attached is the patch for the simple task notifier support that has
been discussed on lse-tech on multiple occasions (it superceeds
pnotify/pagg/task_notify). I provides a way to hook into the fork/exit
etc. places and can be used for things like task grouping and
accounting, but also to clean up all the conditional callouts we have
in the fork/exit paths. I will be posting one example in the next
email and I will be happy to do a bunch more if we can come to
agreement on this approach.

I am using the raw notifier chain to give the clients the same
sleep/blocking rules as the parents currently have. IMHO this makes
the most sense to keep the overhead at a minimum.

Comments/oppinions/flames?

Cheers,
Jes

Simple task notifier support. This uses the raw notifier chain allowing
the users the same calls to sleeping functions as are in fork() etc.

Signed-off-by: Jes Sorensen <je...@sg...>

----

 fs/exec.c                 |    3 +++
 include/linux/init_task.h |    2 ++
 include/linux/notifier.h  |    5 +++++
 include/linux/sched.h     |    3 +++
 kernel/exit.c             |    5 +++++
 kernel/fork.c             |   16 ++++++++++++++++
 6 files changed, 34 insertions(+)

Index: linux-2.6/fs/exec.c
===================================================================
--- linux-2.6.orig/fs/exec.c
+++ linux-2.6/fs/exec.c
@@ -49,6 +49,7 @@
 #include <linux/rmap.h>
 #include <linux/acct.h>
 #include <linux/cn_proc.h>
+#include <linux/notifier.h>
 
 #include <asm/uaccess.h>
 #include <asm/mmu_context.h>
@@ -1001,6 +1002,8 @@
 		suid_keys(current);
 	exec_keys(current);
 
+	raw_notifier_call_chain(&current->task_notifier, TN_EXEC, NULL);
+
 	task_lock(current);
 	unsafe = unsafe_exec(current);
 	security_bprm_apply_creds(bprm, unsafe);
Index: linux-2.6/include/linux/init_task.h
===================================================================
--- linux-2.6.orig/include/linux/init_task.h
+++ linux-2.6/include/linux/init_task.h
@@ -3,6 +3,7 @@
 
 #include <linux/file.h>
 #include <linux/rcupdate.h>
+#include <linux/notifier.h>
 
 #define INIT_FDTABLE \
 {							\
@@ -123,6 +124,7 @@
 	.journal_info	= NULL,						\
 	.cpu_timers	= INIT_CPU_TIMERS(tsk.cpu_timers),		\
 	.fs_excl	= ATOMIC_INIT(0),				\
+	.task_notifier	= RAW_NOTIFIER_INIT(tsk.task_notifier),	\
 }
 
 
Index: linux-2.6/include/linux/notifier.h
===================================================================
--- linux-2.6.orig/include/linux/notifier.h
+++ linux-2.6/include/linux/notifier.h
@@ -154,5 +154,10 @@
 #define CPU_DOWN_FAILED		0x0006 /* CPU (unsigned)v NOT going down */
 #define CPU_DEAD		0x0007 /* CPU (unsigned)v dead */
 
+#define TN_FORK		0x0001	/* Task notifier - fork */
+#define TN_EXIT		0x0002	/* Task notifier - exit */
+#define TN_FREE		0x0003	/* Task notifier - free */
+#define TN_EXEC		0x0004	/* Task notifier - exec */
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_NOTIFIER_H */
Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -36,6 +36,7 @@
 #include <linux/seccomp.h>
 #include <linux/rcupdate.h>
 #include <linux/futex.h>
+#include <linux/notifier.h>
 
 #include <linux/auxvec.h>	/* For AT_VECTOR_SIZE */
 
@@ -888,6 +889,8 @@
 	 * cache last used pipe for splice
 	 */
 	struct pipe_inode_info *splice_pipe;
+
+	struct raw_notifier_head task_notifier;
 };
 
 static inline pid_t process_group(struct task_struct *tsk)
Index: linux-2.6/kernel/exit.c
===================================================================
--- linux-2.6.orig/kernel/exit.c
+++ linux-2.6/kernel/exit.c
@@ -34,6 +34,7 @@
 #include <linux/mutex.h>
 #include <linux/futex.h>
 #include <linux/compat.h>
+#include <linux/notifier.h>
 #include <linux/pipe_fs_i.h>
 
 #include <asm/uaccess.h>
@@ -910,6 +911,10 @@
 	if (unlikely(tsk->compat_robust_list))
 		compat_exit_robust_list(tsk);
 #endif
+	/*
+	 * Must call the exit notifier before losing the mm struct
+	 */
+	raw_notifier_call_chain(&tsk->task_notifier, TN_EXIT, tsk);
 	exit_mm(tsk);
 
 	exit_sem(tsk);
Index: linux-2.6/kernel/fork.c
===================================================================
--- linux-2.6.orig/kernel/fork.c
+++ linux-2.6/kernel/fork.c
@@ -44,6 +44,7 @@
 #include <linux/rmap.h>
 #include <linux/acct.h>
 #include <linux/cn_proc.h>
+#include <linux/notifier.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -114,6 +115,7 @@
 	WARN_ON(atomic_read(&tsk->usage));
 	WARN_ON(tsk == current);
 
+	raw_notifier_call_chain(&tsk->task_notifier, TN_FREE, tsk);
 	if (unlikely(tsk->audit_context))
 		audit_free(tsk);
 	security_task_free(tsk);
@@ -1043,6 +1045,11 @@
 	if (clone_flags & CLONE_THREAD)
 		p->tgid = current->tgid;
 
+	/*
+	 * Any of the below could be trying to use this
+	 */
+	RAW_INIT_NOTIFIER_HEAD(&p->task_notifier);
+
 	if ((retval = security_task_alloc(p)))
 		goto bad_fork_cleanup_policy;
 	if ((retval = audit_alloc(p)))
@@ -1103,6 +1110,14 @@
 	p->exit_state = 0;
 
 	/*
+	 * Call the task notifiers for the current thread. It is their
+	 * job to determine whether or not to preserve the parent's
+	 * task_notifiers.
+	 */
+	if (raw_notifier_call_chain(&current->task_notifier, TN_FORK, p))
+		goto bad_fork_cleanup_namespace;
+
+	/*
 	 * Ok, make it visible to the rest of the system.
 	 * We dont wake it up yet.
 	 */
@@ -1239,6 +1254,7 @@
 	audit_free(p);
 bad_fork_cleanup_security:
 	security_task_free(p);
+	raw_notifier_call_chain(&p->task_notifier, TN_EXIT, p);
 bad_fork_cleanup_policy:
 #ifdef CONFIG_NUMA
 	mpol_free(p->mempolicy);