Pavel Begunkov <asml.silence@xxxxxxxxx> writes: > On 12/24/21 01:34, Olivier Langlois wrote: >> On Fri, 2021-10-22 at 15:13 +0100, Pavel Begunkov wrote: >>> On 6/9/21 21:17, Eric W. Biederman wrote: >>> In short, a task creates an io_uring worker thread, then the worker >>> submits a task_work item to the creator task and won't die until >>> the item is executed/cancelled. And I found that the creator task is >>> sleeping in do_coredump() -> wait_for_completion() >>> > [...] >>> A hack executing tws there helps (see diff below). >>> Any chance anyone knows what this is and how to fix it? >>> > [...] >> Pavel, >> >> I cannot comment on the merit of the proposed hack but my proposed >> patch to fix the coredump truncation issue when a process using >> io_uring core dumps that I submitted back in August is still >> unreviewed! > > That's unfortunate. Not like I can help in any case, but I assumed > it was dealt with by > > commit 06af8679449d4ed282df13191fc52d5ba28ec536 > Author: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> > Date: Thu Jun 10 15:11:11 2021 -0500 > > coredump: Limit what can interrupt coredumps > Olivier Langlois has been struggling with coredumps being incompletely > written in > processes using io_uring. > ... I thought it had been too. >> https://lore.kernel.org/lkml/1625bc89782bf83d9d8c7c63e8ffcb651ccb15fa.1629655338.git.olivier@xxxxxxxxxxxxxx/ >> >> I have been using it since then I must have generated many dozens of >> perfect core dump files with it and I have not seen a single truncated >> core dump files like I used to have prior to the patch. >> >> I am bringing back my patch to your attention because one nice side >> effect of it is that it would have avoided totally the problem that you >> have encountered in coredump_wait() since it does cancel io_uring >> resources before calling coredump_wait()! > > FWIW, I worked it around in io_uring back then by breaking the > dependency. I am in the middle of untangling the dependencies between ptrace, coredump, signal handling and maybe a few related things. Do folks have a reproducer I can look at? Pavel especially if you have something that reproduces on the current kernels. As part of that I am in the process of guaranteeing all of the coredump work happens in get_signal so nothing of io_uring or any cleanup anywhere else runs until the coredump completes. I haven't quite posted the code for review because it's the holidays. But I am aiming at v5.17 or possibly v5.18, as the code is just about ready. Eric
