On Tue, 14 Apr 2020 09:23:40 +0200 Dmitry Vyukov wrote: > > On Mon, Apr 13, 2020 at 10:32 PM Andrew Morton > <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > On Mon, 13 Apr 2020 00:50:11 -0700 syzbot <syzbot+2854d22c7dd957a6519a@sy= > zkaller.appspotmail.com> wrote: > > > > > Hello, > > > > > > syzbot found the following crash on: > > > > > > HEAD commit: ae46d2aa mm/gup: Let __get_user_pages_locked() return -= > EIN.. > > > git tree: upstream > > > console output: https://syzkaller.appspot.com/x/log.txt?x=3D12b60343e00= > 000 > > > kernel config: https://syzkaller.appspot.com/x/.config?x=3Dca75979eeeb= > f06c2 > > > dashboard link: https://syzkaller.appspot.com/bug?extid=3D2854d22c7dd95= > 7a6519a > > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > > > > > Unfortunately, I don't have any reproducer for this crash yet. > > > > > > IMPORTANT: if you fix the bug, please add the following tag to the comm= > it: > > > Reported-by: syzbot+2854d22c7dd957a6519a@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > (cc's added) > > > > Looks like the loop backing device's pagecache still has a dirty page, > > despite us having just run sync_blockdev(). It may well be a race of > > some form - do we have any description of what the test is doing? > > > Yes, it's probably loop related. And this is probably a very hard to > trigger race. > Below are the suspect programs that triggered this. > This also happened on upstream before: > https://syzkaller.appspot.com/bug?id=3D77543faae8aa91ae9993d8e0d34df41926b2= > dc8f > And also on ChromeOS 4.19 and one 4.15 tree. But in all cases the rate > is very low and syzkaller was never able to reproduce this. So I would > assume this is a race with an inconsistency window around few > instructions. But I think it is real because over the past year it > happened 14 times and reports are similar each time and the suspect > programs are similar and there are no red flags in these crashes. If its comment is still correct, is it making sense to lock inode? /** * truncate_inode_pages - truncate *all* the pages from an offset * @mapping: mapping to truncate * @lstart: offset from which to truncate * * Called under (and serialised by) inode->i_mutex. * * Note: When this function returns, there can be a page in the process of * deletion (inside __delete_from_page_cache()) in the specified range. Thus * mapping->nrpages can be non-zero when this function returns even after * truncation of the whole mapping. */ (BTW, a tree-wide cleanup of comment in terms of i_mutex looks needed.) --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -83,7 +83,9 @@ void kill_bdev(struct block_device *bdev return; invalidate_bh_lrus(); + inode_lock(bdev->bd_inode); truncate_inode_pages(mapping, 0); + inode_unlock(bdev->bd_inode); } EXPORT_SYMBOL(kill_bdev);
