[RFC PATCH] vfs: Fix might sleep in load_unaligned_zeropad() with rcu read lock held

[Al Viro]

On Wed, Nov 26, 2025 at 06:19:52PM +0800, Xie Yuanbin wrote:
> When the path is initialized with LOOKUP_RCU flag in path_init(), the
> rcu read lock will be acquired. Inside the rcu critical section,
> load_unaligned_zeropad() may be called. According to the comments of
> load_unaligned_zeropad(), when loading the memory, a page fault may be
> triggered in the very unlikely case.

> Add pagefault_disable() to handle this situation.

Way too costly, IMO.  That needs to be dealt with in page fault handler
and IIRC arm used to do that; did that get broken at some point?