Re: [PATCH v8 13/19] locking/rwsem: Make rwsem->owner an atomic_long_t

From: Waiman Long
Date: Fri Jul 19 2019 - 15:32:15 EST

On 7/19/19 2:45 PM, Luis Henriques wrote:
> On Mon, May 20, 2019 at 04:59:12PM -0400, Waiman Long wrote:
>> The rwsem->owner contains not just the task structure pointer, it also
>> holds some flags for storing the current state of the rwsem. Some of
>> the flags may have to be atomically updated. To reflect the new reality,
>> the owner is now changed to an atomic_long_t type.
>> New helper functions are added to properly separate out the task
>> structure pointer and the embedded flags.
> I started seeing KASAN use-after-free with current master, and a bisect
> showed me that this commit 94a9717b3c40 ("locking/rwsem: Make
> rwsem->owner an atomic_long_t") was the problem. Does it ring any
> bells? I can easily reproduce it with xfstests (generic/464).
> Cheers,
> --
> LuÃs

This patch shouldn't change the behavior of the rwsem code. The code
only access data within the rw_semaphore structures. I don't know why it
will cause a KASAN error. I will have to reproduce it and figure out
exactly which statement is doing the invalid access.