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exec: simplify the new ->sighand allocation

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de_thread() pre-allocates newsighand to make sure that exec() can't fail after
killing all sub-threads. Imho, this buys nothing, but complicates the code:

	- this is (mostly) needed to handle CLONE_SIGHAND without CLONE_THREAD
	  tasks, this is very unlikely (if ever used) case

	- unless we already have some serious problems, GFP_KERNEL allocation
	  should not fail

	- ENOMEM still can happen after de_thread(), ->sighand is not the last
	  object we have to allocate

Change the code to allocate the new ->sighand on demand.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2007-10-16 23:27:22 -07:00 committed by Linus Torvalds
parent 0840a90d94
commit b2c903b879
1 changed files with 9 additions and 15 deletions
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24
fs/exec.c
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@ -747,7 +747,7 @@ static int exec_mmap(struct mm_struct *mm)
static int de_thread(struct task_struct *tsk)
{
struct signal_struct *sig = tsk->signal;
struct sighand_struct *newsighand, *oldsighand = tsk->sighand;
struct sighand_struct *oldsighand = tsk->sighand;
spinlock_t *lock = &oldsighand->siglock;
struct task_struct *leader = NULL;
int count;
@ -761,10 +761,6 @@ static int de_thread(struct task_struct *tsk)
return 0;
}
newsighand = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
if (!newsighand)
return -ENOMEM;
if (thread_group_empty(tsk))
goto no_thread_group;
@ -781,7 +777,6 @@ static int de_thread(struct task_struct *tsk)
*/
spin_unlock_irq(lock);
read_unlock(&tasklist_lock);
kmem_cache_free(sighand_cachep, newsighand);
return -EAGAIN;
}
@ -899,17 +894,16 @@ no_thread_group:
if (leader)
release_task(leader);
if (atomic_read(&oldsighand->count) == 1) {
if (atomic_read(&oldsighand->count) != 1) {
struct sighand_struct *newsighand;
/*
* Now that we nuked the rest of the thread group,
* it turns out we are not sharing sighand any more either.
* So we can just keep it.
*/
kmem_cache_free(sighand_cachep, newsighand);
} else {
/*
* Move our state over to newsighand and switch it in.
* This ->sighand is shared with the CLONE_SIGHAND
* but not CLONE_THREAD task, switch to the new one.
*/
newsighand = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
if (!newsighand)
return -ENOMEM;
atomic_set(&newsighand->count, 1);
memcpy(newsighand->action, oldsighand->action,
sizeof(newsighand->action));