Re: [PATCH] brd: fix sleeping memory allocation in brd_insert_page()

[Tetsuo Handa]

On 2025/06/28 17:36, Tetsuo Handa wrote:
> syzbot is reporting that brd_insert_page() is calling
> __xa_cmpxchg(__GFP_DIRECT_RECLAIM) with spinlock and RCU lock held.

Hmm. Holding spinlock itself is OK because xa_lock() is a requirement.

> Change __xa_cmpxchg() to use GFP_NOWAIT | __GFP_NOWARN, for it is likely
> that __xa_cmpxchg() succeeds because of preceding alloc_page().

Since this gfp flag is for allocating index array, it should use
__GFP_DIRECT_RECLAIM if possible. Then, deferring RCU lock if possible
makes sense. Then, I wonder what this RCU lock is protecting...