6fa9201a89
If a socket redirects to itself and it is under memory pressure it is
possible to get a socket stuck so that recv() returns EAGAIN and the
socket can not advance for some time. This happens because when
redirecting a skb to the same socket we received the skb on we first
check if it is OK to enqueue the skb on the receiving socket by checking
memory limits. But, if the skb is itself the object holding the memory
needed to enqueue the skb we will keep retrying from kernel side
and always fail with EAGAIN. Then userspace will get a recv() EAGAIN
error if there are no skbs in the psock ingress queue. This will continue
until either some skbs get kfree'd causing the memory pressure to
reduce far enough that we can enqueue the pending packet or the
socket is destroyed. In some cases its possible to get a socket
stuck for a noticeable amount of time if the socket is only receiving
skbs from sk_skb verdict programs. To reproduce I make the socket
memory limits ridiculously low so sockets are always under memory
pressure. More often though if under memory pressure it looks like
a spurious EAGAIN error on user space side causing userspace to retry
and typically enough has moved on the memory side that it works.
To fix skip memory checks and skb_orphan if receiving on the same
sock as already assigned.
For SK_PASS cases this is easy, its always the same socket so we
can just omit the orphan/set_owner pair.
For backlog cases we need to check skb->sk and decide if the orphan
and set_owner pair are needed.
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.