On Sun, Feb 09, 2020 at 12:52:51PM +0100, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
The patch below does not apply to the 5.5-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From f0b493e6b9a8959356983f57112229e69c2f7b8c Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@xxxxxxxxx>
Date: Sat, 1 Feb 2020 21:30:11 -0700
Subject: [PATCH] io_uring: prevent potential eventfd recursion on poll
If we have nested or circular eventfd wakeups, then we can deadlock if
we run them inline from our poll waitqueue wakeup handler. It's also
possible to have very long chains of notifications, to the extent where
we could risk blowing the stack.
Check the eventfd recursion count before calling eventfd_signal(). If
it's non-zero, then punt the signaling to async context. This is always
safe, as it takes us out-of-line in terms of stack and locking context.
Cc: stable@xxxxxxxxxxxxxxx # 5.1+
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
I queued it back to 5.5 by taking f2842ab5b72d ("io_uring: enable option
to only trigger eventfd for async completions") and working around
missing commit 69b3e546139a ("io_uring: change io_ring_ctx bool fields
into bit fields"). However, 5.4 is a bit more complex than what I can
tackle without a test suite.
Jens, is there something I can run to validate io_uring on older
kernels?
--
Thanks,
Sasha
