patches/kernel/0007-io_uring-don-t-block-level-reissue-off-completion-pa.patch

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: Fabian Ebner <f.ebner@proxmox.com>
   3 Date: Wed, 28 Jul 2021 08:55:31 +0200
   4 Subject: [PATCH] io_uring: don't block level reissue off completion path
   5
   6 Some setups, like SCSI, can throw spurious -EAGAIN off the softirq
   7 completion path. Normally we expect this to happen inline as part
   8 of submission, but apparently SCSI has a weird corner case where it
   9 can happen as part of normal completions.
  10
  11 This should be solved by having the -EAGAIN bubble back up the stack
  12 as part of submission, but previous attempts at this failed and we're
  13 not just quite there yet. Instead we currently use REQ_F_REISSUE to
  14 handle this case.
  15
  16 For now, catch it in io_rw_should_reissue() and prevent a reissue
  17 from a bogus path.
  18
  19 Upstream mail:
  20 https://lore.kernel.org/io-uring/20210727165811.284510-3-axboe@kernel.dk/T/#u
  21
  22 Originally-by: Jens Axboe <axboe@kernel.dk>
  23 [backport]
  24 Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>
  25 ---
  26  fs/io_uring.c | 7 +++++++
  27  1 file changed, 7 insertions(+)
  28
  29 diff --git a/fs/io_uring.c b/fs/io_uring.c
  30 index 2b86b413641a..11f615033c70 100644
  31 --- a/fs/io_uring.c
  32 +++ b/fs/io_uring.c
  33 @@ -2731,6 +2731,13 @@ static bool io_rw_reissue(struct io_kiocb *req, long res)
  34         if (percpu_ref_is_dying(&req->ctx->refs))
  35                 return false;
  36
  37 +       /*
  38 +        * Play it safe and assume not safe to re-import and reissue if we're
  39 +        * not in the original thread group (or in task context).
  40 +        */
  41 +       if (!same_thread_group(req->task, current) || !in_task())
  42 +               return false;
  43 +
  44         lockdep_assert_held(&req->ctx->uring_lock);
  45
  46         ret = io_sq_thread_acquire_mm_files(req->ctx, req);
  47 --
  48 2.30.2
  49