On Fri, 2016-21-10 at 09:04:17 UTC, Paul Mackerras wrote: > This fixes a race condition where one thread that is entering or > leaving a power-saving state can inadvertently ignore the lock bit > that was set by another thread, and potentially also clear it. > The core_idle_lock_held function is called when the lock bit is > seen to be set. It polls the lock bit until it is clear, then > does a lwarx to load the word containing the lock bit and thread > idle bits so it can be updated. However, it is possible that the > value loaded with the lwarx has the lock bit set, even though an > immediately preceding lwz loaded a value with the lock bit clear. > If this happens then we go ahead and update the word despite the > lock bit being set, and when called from pnv_enter_arch207_idle_mode, > we will subsequently clear the lock bit. > > No identifiable misbehaviour has been attributed to this race. > > This fixes it by checking the lock bit in the value loaded by the > lwarx. If it is set then we just go back and keep on polling. > > Fixes: b32aadc1a8ed > Signed-off-by: Paul Mackerras <pau...@ozlabs.org>
Applied to powerpc fixes, thanks. I added: Cc: sta...@vger.kernel.org # v4.2+ https://git.kernel.org/powerpc/c/09b7e37b18eecc1e347f4b1a3bc863 cheers
