On Tue 31-07-18 00:07:22, Tetsuo Handa wrote: > On 2018/07/21 5:06, Andrew Morton wrote: > > On Fri, 20 Jul 2018 19:36:23 +0900 Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote: > > > >>> > >>> This report is stalling after mount() completed and process used remap_file_pages(). > >>> I think that we might need to use debug printk(). But I don't know what to examine. > >>> > >> > >> Andrew, can you pick up this debug printk() patch? > >> I guess we can get the result within one week. > > > > Sure, let's toss it in -next for a while. > > > >> >From 8f55e00b21fefffbc6abd9085ac503c52a302464 Mon Sep 17 00:00:00 2001 > >> From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> > >> Date: Fri, 20 Jul 2018 19:29:06 +0900 > >> Subject: [PATCH] fs/buffer.c: add debug print for __getblk_gfp() stall problem > >> > >> Among syzbot's unresolved hung task reports, 18 out of 65 reports contain > >> __getblk_gfp() line in the backtrace. Since there is a comment block that > >> says that __getblk_gfp() will lock up the machine if try_to_free_buffers() > >> attempt from grow_dev_page() is failing, let's start from checking whether > >> syzbot is hitting that case. This change will be removed after the bug is > >> fixed. > > > > I'm not sure that grow_dev_page() is hanging. It has often been > > suspected, but always is proven innocent. Lets see. > > syzbot reproduced this problem ( https://syzkaller.appspot.com/text?tag=CrashLog&x=11f2fc44400000 ) . > It says that grow_dev_page() is returning 1 but __find_get_block() is failing forever. Any idea? Looks like some kind of a race where device block size gets changed while getblk() runs (and creates buffers for underlying page). I don't have time to nail it down at this moment can have a look into it later unless someone beats me to it. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
