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Revision cccd32816506cbac3a4c65d9dff51b3125ef1a03 authored by Lukas Wunner on 15 September 2023, 07:55:39 UTC, committed by Ingo Molnar on 15 September 2023, 09:28:08 UTC 
panic: Reenable preemption in WARN slowpath
 
Commit:

  5a5d7e9badd2 ("cpuidle: lib/bug: Disable rcu_is_watching() during WARN/BUG")

amended warn_slowpath_fmt() to disable preemption until the WARN splat
has been emitted.

However the commit neglected to reenable preemption in the !fmt codepath,
i.e. when a WARN splat is emitted without additional format string.

One consequence is that users may see more splats than intended.  E.g. a
WARN splat emitted in a work item results in at least two extra splats:

  BUG: workqueue leaked lock or atomic
  (emitted by process_one_work())

  BUG: scheduling while atomic
  (emitted by worker_thread() -> schedule())

Ironically the point of the commit was to *avoid* extra splats. ;)

Fix it.

Fixes: 5a5d7e9badd2 ("cpuidle: lib/bug: Disable rcu_is_watching() during WARN/BUG")
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/3ec48fde01e4ee6505f77908ba351bad200ae3d1.1694763684.git.lukas@wunner.de
1 parent 9fdfb15
Raw File
epoll.c 
// SPDX-License-Identifier: GPL-2.0
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/uaccess.h>
#include <linux/io_uring.h>
#include <linux/eventpoll.h>

#include <uapi/linux/io_uring.h>

#include "io_uring.h"
#include "epoll.h"

#if defined(CONFIG_EPOLL)
struct io_epoll {
	struct file			*file;
	int				epfd;
	int				op;
	int				fd;
	struct epoll_event		event;
};

int io_epoll_ctl_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
	struct io_epoll *epoll = io_kiocb_to_cmd(req, struct io_epoll);

	if (sqe->buf_index || sqe->splice_fd_in)
		return -EINVAL;

	epoll->epfd = READ_ONCE(sqe->fd);
	epoll->op = READ_ONCE(sqe->len);
	epoll->fd = READ_ONCE(sqe->off);

	if (ep_op_has_event(epoll->op)) {
		struct epoll_event __user *ev;

		ev = u64_to_user_ptr(READ_ONCE(sqe->addr));
		if (copy_from_user(&epoll->event, ev, sizeof(*ev)))
			return -EFAULT;
	}

	return 0;
}

int io_epoll_ctl(struct io_kiocb *req, unsigned int issue_flags)
{
	struct io_epoll *ie = io_kiocb_to_cmd(req, struct io_epoll);
	int ret;
	bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;

	ret = do_epoll_ctl(ie->epfd, ie->op, ie->fd, &ie->event, force_nonblock);
	if (force_nonblock && ret == -EAGAIN)
		return -EAGAIN;

	if (ret < 0)
		req_set_fail(req);
	io_req_set_res(req, ret, 0);
	return IOU_OK;
}
#endif
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