Messages in this thread | | | Subject | Re: [PATCH] mm/vmalloc: Fix unlock order in s_stop() | From | Waiman Long <> | Date | Mon, 14 Dec 2020 10:05:28 -0500 |
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On 12/14/20 4:39 AM, David Hildenbrand wrote: > On 13.12.20 19:08, Waiman Long wrote: >> When multiple locks are acquired, they should be released in reverse >> order. For s_start() and s_stop() in mm/vmalloc.c, that is not the >> case. >> >> s_start: mutex_lock(&vmap_purge_lock); spin_lock(&vmap_area_lock); >> s_stop : mutex_unlock(&vmap_purge_lock); spin_unlock(&vmap_area_lock); >> >> This unlock sequence, though allowed, is not optimal. If a waiter is >> present, mutex_unlock() will need to go through the slowpath of waking >> up the waiter with preemption disabled. Fix that by releasing the >> spinlock first before the mutex. >> >> Fixes: e36176be1c39 ("mm/vmalloc: rework vmap_area_lock") > I'm not sure if this classifies as "Fixes". As you correctly state "is > not optimal". But yeah, releasing a spinlock after releasing a mutex > looks weird already. > Yes, it may not be technically a real bug fix. However, the order just doesn't look right. That is why I sent out a patch to address that.
Cheers, Longman
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