Messages in this thread | | | Date | Fri, 20 May 2022 01:12:04 +0200 | From | "Jason A. Donenfeld" <> | Subject | Re: [PATCH 1/2] random: convert to using fops->read_iter() |
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Hi Jens,
On Thu, May 19, 2022 at 01:31:32PM -0600, Jens Axboe wrote: > for (;;) { > chacha20_block(chacha_state, output); > if (unlikely(chacha_state[12] == 0)) > ++chacha_state[13]; > > block_len = min_t(size_t, len, CHACHA_BLOCK_SIZE); > - left = copy_to_user(ubuf, output, block_len); > - if (left) { > - ret += block_len - left; > + block_len = copy_to_iter(output, block_len, to); > + if (!block_len) > break; > - } > > - ubuf += block_len; > ret += block_len; > len -= block_len; > - if (!len) > - break; > > BUILD_BUG_ON(PAGE_SIZE % CHACHA_BLOCK_SIZE != 0); > if (ret % PAGE_SIZE == 0) { > if (signal_pending(current)) > break; > cond_resched(); > } > }
This isn't quite the same, is it? Before, it would immediately break out of the loop on any short copy. Now, it will only break out on a zero copy, which means it's possible that ret % PAGE_SIZE == 0, and there'll be an unnecessary cond_resched() before copy_to_iter() runs again and then breaks.
Jason
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