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BUG/MEDIUM: mt_list: Make sure not to unlock the element twice

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In mt_list_delete(), if the element was not in a list, then n and p will
point to it, and so setting n->prev and n->next will be enough to unlock it.
Don't do it twice, as once it's been done the first time, another thread may
be working with it, and may have added it to a list already, and doing it
a second time can lead to list inconsistencies.

This should be backported up to 2.8.
This commit is contained in:
Olivier Houchard 2025-10-19 23:17:55 +02:00
parent aa259f5b42
commit 7a33b90b3c
1 changed files with 11 additions and 2 deletions
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13
include/import/mt_list.h
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@ -635,8 +635,17 @@ static MT_INLINE long mt_list_delete(struct mt_list *el)
p->next = n;
__atomic_thread_fence(__ATOMIC_RELEASE);
el->prev = el->next = el;
__atomic_thread_fence(__ATOMIC_RELEASE);
/*
* If the element was not in the list, then n and p
* pointed to it already, and it is unlocked.
* If this is the case, we don't want to do it again,
* because at this point it has been unlocked and
* somebody may be using it already.
*/
if (el != n) {
el->prev = el->next = el;
__atomic_thread_fence(__ATOMIC_RELEASE);
}
if (p != el && n != el)
ret = 1;