[PATCH v2 10/61] kernel/fork: Use maple tree for dup_mmap() during forking
Hillf Danton
hdanton at sina.com
Wed Aug 18 01:36:10 PDT 2021
On Tue, 17 Aug 2021 15:47:11 +0000 Liam R. Howlett wrote:
>
> static inline void mmget(struct mm_struct *mm)
> {
> + mt_set_in_rcu(&mm->mm_mt);
> atomic_inc(&mm->mm_users);
> }
>
> static inline bool mmget_not_zero(struct mm_struct *mm)
> {
> + /*
> + * There is a race below during task tear down that can cause the maple
> + * tree to enter rcu mode with only a single user. If this race
> + * happens, the result would be that the maple tree nodes would remain
> + * active for an extra RCU read cycle.
> + */
> + mt_set_in_rcu(&mm->mm_mt);
> return atomic_inc_not_zero(&mm->mm_users);
> }
Nit, leave the mm with zero refcount intact.
if (atomic_inc_not_zero(&mm->mm_users)) {
mt_set_in_rcu(&mm->mm_mt);
return true;
}
return false;
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