On Mon, Sep 14, 2020 at 03:37:49PM -0700, Linus Torvalds wrote: > > So it _looks_ like this code started using kmap() - probably back when > kmap_atomic() was so cumbersome to use - and was then converted > (conditionally) to kmap_atomic() rather than just changed whole-sale. > Is there actually something that wants to use those sg_miter functions > and sleep? I dug up the old zinc patch submissions and this wasn't present at all in the original. The original zinc code used blkcipher_walk which unconditinoally does kmap_atomic. So it's only the SG miter conversion that introduced this change, which appears to be a simple oversight (I think Ard was working on latency issues at that time, perhaps he was worried about keeping preemption off unnecessarily). ---8<--- There is no reason for the chacha20poly1305 SG miter code to use kmap instead of kmap_atomic as the critical section doesn't sleep anyway. So we can simply get rid of the preemptible check and set SG_MITER_ATOMIC unconditionally. Even if we need to reenable preemption to lower latency we should be doing that by interrupting the SG miter walk rather than using kmap. Reported-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> diff --git a/lib/crypto/chacha20poly1305.c b/lib/crypto/chacha20poly1305.c index 431e04280332..5850f3b87359 100644 --- a/lib/crypto/chacha20poly1305.c +++ b/lib/crypto/chacha20poly1305.c @@ -251,9 +251,7 @@ bool chacha20poly1305_crypt_sg_inplace(struct scatterlist *src, poly1305_update(&poly1305_state, pad0, 0x10 - (ad_len & 0xf)); } - flags = SG_MITER_TO_SG; - if (!preemptible()) - flags |= SG_MITER_ATOMIC; + flags = SG_MITER_TO_SG | SG_MITER_ATOMIC; sg_miter_start(&miter, src, sg_nents(src), flags); -- Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
