From 3aa62497594430ea522050b75c033f71f2c60ee6 Mon Sep 17 00:00:00 2001 From: Lai Jiangshan Date: Tue, 18 Sep 2012 10:40:00 -0700 Subject: [PATCH] workqueue: fix possible stall on try_to_grab_pending() of a delayed work item Currently, when try_to_grab_pending() grabs a delayed work item, it leaves its linked work items alone on the delayed_works. The linked work items are always NO_COLOR and will cause future cwq_activate_first_delayed() increase cwq->nr_active incorrectly, and may cause the whole cwq to stall. For example, state: cwq->max_active = 1, cwq->nr_active = 1 one work in cwq->pool, many in cwq->delayed_works. step1: try_to_grab_pending() removes a work item from delayed_works but leaves its NO_COLOR linked work items on it. step2: Later on, cwq_activate_first_delayed() activates the linked work item increasing ->nr_active. step3: cwq->nr_active = 1, but all activated work items of the cwq are NO_COLOR. When they finish, cwq->nr_active will not be decreased due to NO_COLOR, and no further work items will be activated from cwq->delayed_works. the cwq stalls. Fix it by ensuring the target work item is activated before stealing PENDING in try_to_grab_pending(). This ensures that all the linked work items are activated without incorrectly bumping cwq->nr_active. tj: Updated comment and description. Signed-off-by: Lai Jiangshan Signed-off-by: Tejun Heo Cc: stable@kernel.org --- Reading git-format-patch failed