On 2018/08/06 19:09, Jan Kara wrote: > 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. I feel that the frequency of hitting this problem was decreased by merging loop module's ioctl() serialization patches. But this problem is still there, and syzbot got a new line in https://syzkaller.appspot.com/text?tag=CrashLog&x=177f889f400000 . [ 615.881781] __loop_clr_fd: partition scan of loop5 failed (rc=-22) [ 619.059920] syz-executor4(2193): getblk(): executed=cd bh_count=0 bh_state=29 [ 622.069808] syz-executor4(2193): getblk(): executed=9 bh_count=0 bh_state=0 [ 625.080013] syz-executor4(2193): getblk(): executed=9 bh_count=0 bh_state=0 [ 628.089900] syz-executor4(2193): getblk(): executed=9 bh_count=0 bh_state=0 I guess that loop module is somehow related to this problem.
