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author | Oleg Nesterov <oleg@redhat.com> | 2010-08-10 18:03:07 -0700 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2010-08-11 08:59:19 -0700 |
commit | c7e49c1488ab20342eaaf38f1ca35a207f4c051d (patch) | |
tree | 43876a69cafbb49ce86f71ba5db88018ca7cc036 /kernel | |
parent | 13d7e3a2dba6a79589ed34dc0b9114d7b5ff9eab (diff) | |
download | kernel_samsung_crespo-c7e49c1488ab20342eaaf38f1ca35a207f4c051d.zip kernel_samsung_crespo-c7e49c1488ab20342eaaf38f1ca35a207f4c051d.tar.gz kernel_samsung_crespo-c7e49c1488ab20342eaaf38f1ca35a207f4c051d.tar.bz2 |
ptrace: optimize exit_ptrace() for the likely case
exit_ptrace() takes tasklist_lock unconditionally. We need this lock to
avoid the race with ptrace_traceme(), it acts as a barrier.
Change its caller, forget_original_parent(), to call exit_ptrace() under
tasklist_lock. Change exit_ptrace() to drop and reacquire this lock if
needed.
This allows us to add the fastpath list_empty(ptraced) check. In the
likely no-tracees case exit_ptrace() just returns and we avoid the lock()
+ unlock() sequence.
"Zhang, Yanmin" <yanmin_zhang@linux.intel.com> suggested to add this
check, and he reports that this change adds about 11% improvement in some
tests.
Suggested-and-tested-by: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/exit.c | 7 | ||||
-rw-r--r-- | kernel/ptrace.c | 12 |
2 files changed, 14 insertions, 5 deletions
diff --git a/kernel/exit.c b/kernel/exit.c index ceffc67..671ed56 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -771,9 +771,12 @@ static void forget_original_parent(struct task_struct *father) struct task_struct *p, *n, *reaper; LIST_HEAD(dead_children); - exit_ptrace(father); - write_lock_irq(&tasklist_lock); + /* + * Note that exit_ptrace() and find_new_reaper() might + * drop tasklist_lock and reacquire it. + */ + exit_ptrace(father); reaper = find_new_reaper(father); list_for_each_entry_safe(p, n, &father->children, sibling) { diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 74a3d69..f34d798 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -324,26 +324,32 @@ int ptrace_detach(struct task_struct *child, unsigned int data) } /* - * Detach all tasks we were using ptrace on. + * Detach all tasks we were using ptrace on. Called with tasklist held + * for writing, and returns with it held too. But note it can release + * and reacquire the lock. */ void exit_ptrace(struct task_struct *tracer) { struct task_struct *p, *n; LIST_HEAD(ptrace_dead); - write_lock_irq(&tasklist_lock); + if (likely(list_empty(&tracer->ptraced))) + return; + list_for_each_entry_safe(p, n, &tracer->ptraced, ptrace_entry) { if (__ptrace_detach(tracer, p)) list_add(&p->ptrace_entry, &ptrace_dead); } - write_unlock_irq(&tasklist_lock); + write_unlock_irq(&tasklist_lock); BUG_ON(!list_empty(&tracer->ptraced)); list_for_each_entry_safe(p, n, &ptrace_dead, ptrace_entry) { list_del_init(&p->ptrace_entry); release_task(p); } + + write_lock_irq(&tasklist_lock); } int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len) |