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I hit a very bad problem during my tests of SENDMSG_ZC. BUG(); in first_iovec_segment() triggered very easily. The problem was io_setup_async_msg() in the partial retry case, which seems to happen more often with _ZC. iov_iter_iovec_advance() may change i->iov in order to have i->iov_offset being only relative to the first element. Which means kmsg->msg.msg_iter.iov is no longer the same as kmsg->fast_iov. But this would rewind the copy to be the start of async_msg->fast_iov, which means the internal state of sync_msg->msg.msg_iter is inconsitent. I tested with 5 vectors with length like this 4, 0, 64, 20, 8388608 and got a short writes with: - ret=2675244 min_ret=8388692 => remaining 5713448 sr->done_io=2675244 - ret=-EAGAIN => io_uring_poll_arm - ret=4911225 min_ret=5713448 => remaining 802223 sr->done_io=7586469 - ret=-EAGAIN => io_uring_poll_arm - ret=802223 min_ret=802223 => res=8388692 While this was easily triggered with SENDMSG_ZC (queued for 6.1), it was a potential problem starting with7ba89d2af1in 5.18 for IORING_OP_RECVMSG. And also with4c3c09439cin 5.19 for IORING_OP_SENDMSG. However257e84a537introduced the critical code into io_setup_async_msg() in 5.11. Fixes:7ba89d2af1("io_uring: ensure recv and recvmsg handle MSG_WAITALL correctly") Fixes:257e84a537("io_uring: refactor sendmsg/recvmsg iov managing") Cc: stable@vger.kernel.org Signed-off-by: Stefan Metzmacher <metze@samba.org> Reviewed-by: Pavel Begunkov <asml.silence@gmail.com> Link: https://lore.kernel.org/r/b2e7be246e2fb173520862b0c7098e55767567a2.1664436949.git.metze@samba.org Signed-off-by: Jens Axboe <axboe@kernel.dk>
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.