4.12-stable review patch. If anyone has any objections, please let me know.
------------------ From: Kirill Tkhai <[email protected]> commit a0c4acd2c220376b4e9690e75782d0c0afdaab9f upstream. If a writer could been woken up, the above branch if (sem->count == 0) break; would have moved us to taking the sem. So, it's not the time to wake a writer now, and only readers are allowed now. Thus, 0 must be passed to __rwsem_do_wake(). Next, __rwsem_do_wake() wakes readers unconditionally. But we mustn't do that if the sem is owned by writer in the moment. Otherwise, writer and reader own the sem the same time, which leads to memory corruption in callers. rwsem-xadd.c does not need that, as: 1) the similar check is made lockless there, 2) in __rwsem_mark_wake::try_reader_grant we test, that sem is not owned by writer. Signed-off-by: Kirill Tkhai <[email protected]> Acked-by: Peter Zijlstra <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Niklas Cassel <[email protected]> Cc: Peter Zijlstra (Intel) <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Fixes: 17fcbd590d0c "locking/rwsem: Fix down_write_killable() for CONFIG_RWSEM_GENERIC_SPINLOCK=y" Link: http://lkml.kernel.org/r/149762063282.19811.9129615532201147826.stgit@localhost.localdomain Signed-off-by: Ingo Molnar <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- kernel/locking/rwsem-spinlock.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/kernel/locking/rwsem-spinlock.c +++ b/kernel/locking/rwsem-spinlock.c @@ -231,8 +231,8 @@ int __sched __down_write_common(struct r out_nolock: list_del(&waiter.list); - if (!list_empty(&sem->wait_list)) - __rwsem_do_wake(sem, 1); + if (!list_empty(&sem->wait_list) && sem->count >= 0) + __rwsem_do_wake(sem, 0); raw_spin_unlock_irqrestore(&sem->wait_lock, flags); return -EINTR;
