io_uring: check if we need to reschedule during overflow flush

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: io_uring: check if we need to reschedule during overflow flush In terms of normal application usage, this list will always be empty. And if an application does overflow a bit, it'll have a few entries. However, nothing obviously prevents syzbot from running a test case that generates a ton of overflow entries, and then flushing them can take quite a while. Check for needing to reschedule while flushing, and drop our locks and do so if necessary. There's no state to maintain here as overflows always prune from head-of-list, hence it's fine to drop and reacquire the locks at the end of the loop.

References

• https://git.kernel.org/stable/c/a2493904e95ce94bbec819d8f7f03b99976eb25c
• https://git.kernel.org/stable/c/f4ce3b5d26ce149e77e6b8e8f2058aa80e5b034e
• https://git.kernel.org/stable/c/c2eadeafce2d385b3f6d26a7f31fee5aba2bbbb0
• https://git.kernel.org/stable/c/eac2ca2d682f94f46b1973bdf5e77d85d77b8e53