On 6/9/21 21:17, Eric W. Biederman wrote:

quoted

Folks,

Olivier Langlois has been struggling with coredumps getting
truncated in
tasks using io_uring.  He has also apparently been struggling with
the some of his email messages not making it to the lists.

Looks syzbot hit something relevant, see
https://lore.kernel.org/io-
uring/0000000000000012fb05cee99477@google.com/

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()

0xffffffff81343ccb is in do_coredump (fs/coredump.c:469).
464
465             if (core_waiters > 0) {
466                     struct core_thread *ptr;
467
468                     freezer_do_not_count();
469                     wait_for_completion(&core_state->startup);
470                     freezer_count();


A hack executing tws there helps (see diff below).
Any chance anyone knows what this is and how to fix it?

diff --git a/fs/coredump.c b/fs/coredump.c
index 3224dee44d30..f6f9dfb02296 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c

@@ -466,7 +466,8 @@ static int coredump_wait(int exit_code, struct

core_state *core_state)
          struct core_thread *ptr;
  
          freezer_do_not_count();
-        wait_for_completion(&core_state->startup);
+        while (wait_for_completion_interruptible(&core_state-

quoted

startup))

+            tracehook_notify_signal();
          freezer_count();
          /*
           * Wait for all the threads to become inactive, so that