Re: [PATCH 2/2] nvme: drop WARN_ON_ONCE on write_stream bounds check

[Keith Busch]

On Sat, Jul 25, 2026 at 03:51:11PM +0200, Hari Mishal wrote:
> write_stream is validated against bdev_max_write_streams() in both
> generic block direct I/O (block/fops.c) and F2FS before a bio
> carrying it is ever built, so write_stream > nr_plids shouldn't be
> reachable through any current legitimate path. The remaining users
> of bio->bi_write_stream elsewhere in the block layer only copy an
> already-validated value between bios (bio.c, blk-crypto-fallback.c)
> or compare it for merge eligibility (blk-merge.c); none of them
> introduce a new, unvalidated value.
> 
> Using WARN_ON_ONCE as the backstop for that assumption isn't worth
> it given how many deployed systems run with panic-on-warn enabled;
> the existing graceful return BLK_STS_INVAL already handles it on
> its own.

That's not a very good reason to remove a WARN_ON. You've left the check
in for a condition that should never happen, so when it does happen,
it'll be impossible to debug without the WARN.

And the WARN also annotates the branch as unlikely, which is desirable
for this case.