Messages in this thread | | | Date | Tue, 26 Apr 2022 11:43:38 +1000 | Subject | Re: [PATCH v8 01/10] kernfs: Remove reference counting for kernfs_open_node. | From | Imran Khan <> |
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Hello Tejun,
On 23/4/22 2:03 am, Tejun Heo wrote: > On Sun, Apr 10, 2022 at 12:37:10PM +1000, Imran Khan wrote: >> @@ -768,15 +765,15 @@ void kernfs_drain_open_files(struct kernfs_node *kn) >> if (!(kn->flags & (KERNFS_HAS_MMAP | KERNFS_HAS_RELEASE))) >> return; >> >> - spin_lock_irq(&kernfs_open_node_lock); >> on = kn->attr.open; >> - if (on) >> - atomic_inc(&on->refcnt); >> - spin_unlock_irq(&kernfs_open_node_lock); >> if (!on) >> return; >> >> mutex_lock(&kernfs_open_file_mutex); >> + if (!kn->attr.open) { >> + mutex_unlock(&kernfs_open_file_mutex); >> + return; >> + } > > What if @on got freed and new one got allocated between the lockless check > and the locked check? Is there a reason to keep the lockless check at all? >
The only reason for lockless check is to opportunistically check and return if ->attr.open is already NULL, without waiting to acquire the mutex. This is because no one will be adding to ->attr.open at this point of time. But we can live with just the locked check as well. Please let me know if you think of lockless check as an overkill in this case.
Thanks -- Imran
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