On Sat, 2015-03-07 at 13:17 -0500, Sasha Levin wrote: > On 03/07/2015 02:45 AM, Jason Low wrote: > > Fixes tip commit b3fd4f03ca0b (locking/rwsem: Avoid deceiving lock > > spinners). > > > > Ming reported soft lockups occurring when running xfstest due to > > commit b3fd4f03ca0b. > > > > When doing optimistic spinning in rwsem, threads should stop spinning when > > the lock owner is not running. While a thread is spinning on owner, if > > the owner reschedules, owner->on_cpu returns false and we stop spinning. > > > > However, commit b3fd4f03ca0b essentially caused the check to get ignored > > because when we break out of the spin loop due to !on_cpu, we continue > > spinning if sem->owner != NULL. > > > > This patch fixes this by making sure we stop spinning if the owner is not > > running. Furthermore, just like with mutexes, refactor the code such that > > we don't have separate checks for owner_running(). This makes it more > > straightforward in terms of why we exit the spin on owner loop and we > > would also avoid needing to "guess" why we broke out of the loop to make > > this more readable. > > That seems to solve the hangs I'm seeing as well.
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