either bug or unnecessary code in exit_mm()

From: Christopher Friesen
Date: Thu Mar 23 2006 - 16:31:55 EST

In the last few kernels (at least as far back as 2.6.10), exit_mm() looks like this:

static void exit_mm(struct task_struct * tsk)
struct mm_struct *mm = tsk->mm;

mm_release(tsk, mm);
if (!mm)

while mm_release() looks like this:

void mm_release(struct task_struct *tsk, struct mm_struct *mm)
if (tsk->clear_child_tid && atomic_read(&mm->mm_users) > 1) {

If it's valid to call exit_mm() with tsk->mm being NULL, then it seems like we'll get problems when we dereference it unconditionally in mm_release().

If mm_release() is valid, then the check for !mm in exit_mm() is unnecessary but there should probably be a comment.

Can someone tell me which one it is?


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