On Fri, 2021-12-24 at 10:37 +0000, Pavel Begunkov wrote: > 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. > ... > It was a partial fix only. Oleg Nesterov pointed out that the fix was not good if if the core dump was written into a pipe. https://lore.kernel.org/io-uring/20210614141032.GA13677@xxxxxxxxxx/ > > https://lore.kernel.org/lkml/1625bc89782bf83d9d8c7c63e8ffcb651ccb15 > > fa.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. > Yes I have seen your work to fix the problem. It just seems to me that there is no good reason to keep io_uring process requests once you are generating a core dump and simply cancelling io_uring before generating the core dump would have avoided the problem that you have encountered plus any other similar issues yet to come... Greetings,
