Cc: Michal On 2/26/21 2:44 PM, Shakeel Butt wrote: > On Fri, Feb 26, 2021 at 2:09 PM syzbot > <syzbot+506c8a2a115201881d45@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: <snip> >> other info that might help us debug this: >> >> Possible interrupt unsafe locking scenario: >> >> CPU0 CPU1 >> ---- ---- >> lock(hugetlb_lock); >> local_irq_disable(); >> lock(slock-AF_INET); >> lock(hugetlb_lock); >> <Interrupt> >> lock(slock-AF_INET); >> >> *** DEADLOCK *** > > This has been reproduced on 4.19 stable kernel as well [1] and there > is a reproducer as well. > > It seems like sendmsg(MSG_ZEROCOPY) from a buffer backed by hugetlb. I > wonder if we just need to make hugetlb_lock softirq-safe. > > [1] https://syzkaller.appspot.com/bug?extid=6383ce4b0b8ec575ad93 Thanks Shakeel, Commit c77c0a8ac4c5 ("mm/hugetlb: defer freeing of huge pages if in non-task context") attempted to address this issue. It uses a work queue to acquire hugetlb_lock if the caller is !in_task(). In another recent thread, there was the suggestion to change the !in_task to in_atomic. I need to do some research on the subtle differences between in_task, in_atomic, etc. TBH, I 'thought' !in_task would prevent the issue reported here. But, that obviously is not the case. -- Mike Kravetz
