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Date: Thu, 19 May 2022 16:14:17 -0700 From: Tadeusz Struk <tadeusz.struk@...aro.org> To: Jan Kara <jack@...e.cz> Cc: linux-ext4@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>, linux-fsdevel@...r.kernel.org Subject: Re: kernel BUG in ext4_writepages On 5/19/22 05:23, Jan Kara wrote: > Hi! > > On Tue 10-05-22 15:28:38, Tadeusz Struk wrote: >> Syzbot found another BUG in ext4_writepages [1]. >> This time it complains about inode with inline data. >> C reproducer can be found here [2] >> I was able to trigger it on 5.18.0-rc6 >> >> [1] https://syzkaller.appspot.com/bug?id=a1e89d09bbbcbd5c4cb45db230ee28c822953984 >> [2] https://syzkaller.appspot.com/text?tag=ReproC&x=129da6caf00000 > > Thanks for report. This should be fixed by: > > https://lore.kernel.org/all/20220516012752.17241-1-yebin10@huawei.com/ In case of the syzbot bug there is something messed up with PAGE DIRTY flags and the way syzbot sets up the write. This is what triggers the crash: $ ftrace -f ./repro ... [pid 2395] open("./bus", O_RDWR|O_CREAT|O_SYNC|O_NOATIME, 000 <unfinished ...> [pid 2395] <... open resumed> ) = 6 ... [pid 2395] write(6, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 22 <unfinished ...> ... [pid 2395] <... write resumed> ) = 22 One way I could fix it was to clear the PAGECACHE_TAG_DIRTY on the mapping in ext4_try_to_write_inline_data() after the page has been updated: diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c index 9c076262770d..e4bbb53fa26f 100644 --- a/fs/ext4/inline.c +++ b/fs/ext4/inline.c @@ -715,6 +715,7 @@ int ext4_try_to_write_inline_data(struct address_space *mapping, put_page(page); goto out_up_read; } + __xa_clear_mark(&mapping->i_pages, 0, PAGECACHE_TAG_DIRTY); } ret = 1; Please let me know it if makes sense any I will send a proper patch. -- Thanks, Tadeusz
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