From 2f588cee24caf01c1ac08fff90d67c6af555e7c7 Mon Sep 17 00:00:00 2001 From: Dmitry Safonov Date: Thu, 1 Nov 2018 00:24:52 +0000 Subject: [PATCH] tty/ldsem: Decrement wait_readers on timeouted down_read() It seems like when ldsem_down_read() fails with timeout, it misses update for sem->wait_readers. By that reason, when writer finally releases write end of the semaphore __ldsem_wake_readers() does adjust sem->count with wrong value: sem->wait_readers * (LDSEM_ACTIVE_BIAS - LDSEM_WAIT_BIAS) I.e, if update comes with 1 missed wait_readers decrement, sem->count will be 0x100000001 which means that there is active reader and it'll make any further writer to fail in acquiring the semaphore. It looks like, this is a dead-code, because ldsem_down_read() is never called with timeout different than MAX_SCHEDULE_TIMEOUT, so it might be worth to delete timeout parameter and error path fall-back.. Cc: Jiri Slaby Signed-off-by: Dmitry Safonov Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_ldsem.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/tty/tty_ldsem.c b/drivers/tty/tty_ldsem.c index d4d0dbf4a6d9..717292c1c0df 100644 --- a/drivers/tty/tty_ldsem.c +++ b/drivers/tty/tty_ldsem.c @@ -212,6 +212,7 @@ down_read_failed(struct ld_semaphore *sem, long count, long timeout) raw_spin_lock_irq(&sem->wait_lock); if (waiter.task) { atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count); + sem->wait_readers--; list_del(&waiter.list); raw_spin_unlock_irq(&sem->wait_lock); put_task_struct(waiter.task);