From: Jan Kara Date: Thu, 3 May 2018 16:26:26 +0000 (+0200) Subject: bdi: Fix oops in wb_workfn() X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=683b4520d07e4f2e22d5ccab96f67f87b18b98f1;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git bdi: Fix oops in wb_workfn() commit b8b784958eccbf8f51ebeee65282ca3fd59ea391 upstream. Syzbot has reported that it can hit a NULL pointer dereference in wb_workfn() due to wb->bdi->dev being NULL. This indicates that wb_workfn() was called for an already unregistered bdi which should not happen as wb_shutdown() called from bdi_unregister() should make sure all pending writeback works are completed before bdi is unregistered. Except that wb_workfn() itself can requeue the work with: mod_delayed_work(bdi_wq, &wb->dwork, 0); and if this happens while wb_shutdown() is waiting in: flush_delayed_work(&wb->dwork); the dwork can get executed after wb_shutdown() has finished and bdi_unregister() has cleared wb->bdi->dev. Make wb_workfn() use wakeup_wb() for requeueing the work which takes all the necessary precautions against racing with bdi unregistration. CC: Tetsuo Handa CC: Tejun Heo Fixes: 839a8e8660b6777e7fe4e80af1a048aebe2b5977 Reported-by: syzbot Reviewed-by: Dave Chinner Signed-off-by: Jan Kara Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 8a7ef9378bf6..3244932f4d5c 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -1940,7 +1940,7 @@ void wb_workfn(struct work_struct *work) } if (!list_empty(&wb->work_list)) - mod_delayed_work(bdi_wq, &wb->dwork, 0); + wb_wakeup(wb); else if (wb_has_dirty_io(wb) && dirty_writeback_interval) wb_wakeup_delayed(wb);