From 5497d74e75f8b33bc0777d3550c0159b66f0d3fa Mon Sep 17 00:00:00 2001 From: Kirill Tkhai Date: Fri, 16 Jun 2017 16:44:34 +0300 Subject: [PATCH] locking/rwsem-spinlock: Fix EINTR branch in __down_write_common() 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 Acked-by: Peter Zijlstra Cc: Linus Torvalds Cc: Niklas Cassel Cc: Peter Zijlstra (Intel) Cc: Peter Zijlstra Cc: Thomas Gleixner 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 Signed-off-by: Greg Kroah-Hartman --- kernel/locking/rwsem-spinlock.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/locking/rwsem-spinlock.c b/kernel/locking/rwsem-spinlock.c index 2bef4ab94003..a608f7a8fbd1 100644 --- a/kernel/locking/rwsem-spinlock.c +++ b/kernel/locking/rwsem-spinlock.c @@ -233,8 +233,8 @@ int __sched __down_write_common(struct rw_semaphore *sem, int state) 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; -- 2.20.1