The patch titled
pid: Implement transfer_pid and use it to simplify de_thread
has been added to the -mm tree. Its filename is
pid-implement-transfer_pid-and-use-it-to-simplify-de_thread.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: pid: Implement transfer_pid and use it to simplify de_thread
From: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
In de_thread we move pids from one process to another, a rather ugly case.
The function transfer_pid makes it clear what we are doing, and makes the
action atomic. This is useful we ever want to atomically traverse the
process group and session lists, in a rcu safe manner.
Even if the atomic properties this change should be a win as transfer_pid
should be less code to execute than executing both attach_pid and
detach_pid, and this should make de_thread slightly smaller as only a
single function call needs to be emitted. The only downside is that the
code might be slower to execute as the odds are against transfer_pid being
in cache.
Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
fs/exec.c | 11 ++++-------
include/linux/pid.h | 2 ++
kernel/pid.c | 9 +++++++++
3 files changed, 15 insertions(+), 7 deletions(-)
diff -puN fs/exec.c~pid-implement-transfer_pid-and-use-it-to-simplify-de_thread fs/exec.c
--- a/fs/exec.c~pid-implement-transfer_pid-and-use-it-to-simplify-de_thread
+++ a/fs/exec.c
@@ -698,23 +698,20 @@ static int de_thread(struct task_struct
*/
/* Become a process group leader with the old leader's pid.
- * Note: The old leader also uses thispid until release_task
+ * The old leader becomes a thread of the this thread group.
+ * Note: The old leader also uses this pid until release_task
* is called. Odd but simple and correct.
*/
detach_pid(current, PIDTYPE_PID);
current->pid = leader->pid;
attach_pid(current, PIDTYPE_PID, current->pid);
- attach_pid(current, PIDTYPE_PGID, current->signal->pgrp);
- attach_pid(current, PIDTYPE_SID, current->signal->session);
+ transfer_pid(leader, current, PIDTYPE_PGID);
+ transfer_pid(leader, current, PIDTYPE_SID);
list_replace_rcu(&leader->tasks, ¤t->tasks);
current->group_leader = current;
leader->group_leader = current;
- /* Reduce leader to a thread */
- detach_pid(leader, PIDTYPE_PGID);
- detach_pid(leader, PIDTYPE_SID);
-
current->exit_signal = SIGCHLD;
BUG_ON(leader->exit_state != EXIT_ZOMBIE);
diff -puN include/linux/pid.h~pid-implement-transfer_pid-and-use-it-to-simplify-de_thread include/linux/pid.h
--- a/include/linux/pid.h~pid-implement-transfer_pid-and-use-it-to-simplify-de_thread
+++ a/include/linux/pid.h
@@ -76,6 +76,8 @@ extern int FASTCALL(attach_pid(struct ta
enum pid_type type, int nr));
extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));
+extern void FASTCALL(transfer_pid(struct task_struct *old,
+ struct task_struct *new, enum pid_type));
/*
* look up a PID in the hash table. Must be called with the tasklist_lock
diff -puN kernel/pid.c~pid-implement-transfer_pid-and-use-it-to-simplify-de_thread kernel/pid.c
--- a/kernel/pid.c~pid-implement-transfer_pid-and-use-it-to-simplify-de_thread
+++ a/kernel/pid.c
@@ -252,6 +252,15 @@ void fastcall detach_pid(struct task_str
free_pid(pid);
}
+/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
+void fastcall transfer_pid(struct task_struct *old, struct task_struct *new,
+ enum pid_type type)
+{
+ new->pids[type].pid = old->pids[type].pid;
+ hlist_replace_rcu(&old->pids[type].node, &new->pids[type].node);
+ old->pids[type].pid = NULL;
+}
+
struct task_struct * fastcall pid_task(struct pid *pid, enum pid_type type)
{
struct task_struct *result = NULL;
_
Patches currently in -mm which might be from ebiederm@xxxxxxxxxxxx are
i386-kexec-allow-the-kexec-on-panic-support-to-compile-on-voyager.patch
msi-only-keep-one-msi_desc-in-each-slab-entry.patch
msi-use-kmem_cache_zalloc.patch
sysctl-allow-proc-sys-without-sys_sysctl.patch
sysctl-scream-if-someone-uses-sys_sysctl.patch
sysctl-document-that-sys_sysctl-will-be-removed.patch
pid-implement-transfer_pid-and-use-it-to-simplify-de_thread.patch
proc-sysctl-add-_proc_do_string-helper.patch
namespaces-add-nsproxy.patch
namespaces-add-nsproxy-dont-include-compileh.patch
namespaces-incorporate-fs-namespace-into-nsproxy.patch
namespaces-utsname-introduce-temporary-helpers.patch
namespaces-utsname-switch-to-using-uts-namespaces.patch
namespaces-utsname-use-init_utsname-when-appropriate.patch
namespaces-utsname-implement-utsname-namespaces.patch
namespaces-utsname-sysctl-hack.patch
namespaces-utsname-remove-system_utsname.patch
namespaces-utsname-implement-clone_newuts-flag.patch
uts-copy-nsproxy-only-when-needed.patch
ipc-namespace-core.patch
ipc-namespace-utils.patch
genirq-irq-convert-the-move_irq-flag-from-a-32bit-word-to-a-single-bit.patch
genirq-irq-add-moved_masked_irq.patch
genirq-x86_64-irq-reenable-migrating-irqs-to-other-cpus.patch
genirq-msi-simplify-msi-enable-and-disable.patch
genirq-msi-make-the-msi-boolean-tests-return-either-0-or-1.patch
genirq-msi-implement-helper-functions-read_msi_msg-and-write_msi_msg.patch
genirq-msi-refactor-the-msi_ops.patch
genirq-msi-simplify-the-msi-irq-limit-policy.patch
genirq-irq-add-a-dynamic-irq-creation-api.patch
genirq-ia64-irq-dynamic-irq-support.patch
genirq-i386-irq-dynamic-irq-support.patch
genirq-x86_64-irq-dynamic-irq-support.patch
genirq-msi-make-the-msi-code-irq-based-and-not-vector-based.patch
genirq-x86_64-irq-move-msi-message-composition-into-io_apicc.patch
genirq-i386-irq-move-msi-message-composition-into-io_apicc.patch
genirq-msi-only-build-msi-apicc-on-ia64.patch
genirq-msi-only-build-msi-apicc-on-ia64-fix.patch
genirq-x86_64-irq-remove-the-msi-assumption-that-irq-==-vector.patch
genirq-i386-irq-remove-the-msi-assumption-that-irq-==-vector.patch
genirq-irq-remove-msi-hacks.patch
genirq-irq-generalize-the-check-for-hardirq_bits.patch
genirq-x86_64-irq-make-the-external-irq-handlers-report-their-vector-not-the-irq-number.patch
genirq-x86_64-irq-make-vector_irq-per-cpu.patch
genirq-x86_64-irq-kill-gsi_irq_sharing.patch
genirq-x86_64-irq-kill-irq-compression.patch
add-hypertransport-capability-defines.patch
add-hypertransport-capability-defines-fix.patch
initial-generic-hypertransport-interrupt-support.patch
pidhash-temporary-debug-checks.patch
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