b19062a567
If we have multiple threads, one doing io_uring_enter() while the other is doing io_uring_register(), we can run into a deadlock between the two. io_uring_register() must wait for existing users of the io_uring instance to exit. But it does so while holding the io_uring mutex. Callers of io_uring_enter() may need this mutex to make progress (and eventually exit). If we wait for users to exit in io_uring_register(), we can't do so with the io_uring mutex held without potentially risking a deadlock. Drop the io_uring mutex while waiting for existing callers to exit. This is safe and guaranteed to make forward progress, since we already killed the percpu ref before doing so. Hence later callers of io_uring_enter() will be rejected. Reported-by: syzbot+16dc03452dee970a0c3e@syzkaller.appspotmail.com 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.