Messages in this thread | | | Subject | Re: [PATCH v4 2/5] locking/rwsem: Protect all writes to owner by WRITE_ONCE | From | Jason Low <> | Date | Wed, 18 May 2016 10:21:35 -0700 |
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On Wed, 2016-05-18 at 07:04 -0700, Davidlohr Bueso wrote: > On Tue, 17 May 2016, Waiman Long wrote: > > >Without using WRITE_ONCE(), the compiler can potentially break a > >write into multiple smaller ones (store tearing). So a read from the > >same data by another task concurrently may return a partial result. > >This can result in a kernel crash if the data is a memory address > >that is being dereferenced. > > > >This patch changes all write to rwsem->owner to use WRITE_ONCE() > >to make sure that store tearing will not happen. READ_ONCE() may > >not be needed for rwsem->owner as long as the value is only used for > >comparison and not dereferencing.
It might be okay to leave out READ_ONCE() for reading rwsem->owner, but couldn't we include it to at least document that we're performing a "special" lockless read?
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