Re: [PATCH v7 1/3] bio: limit bio max size
From: Bart Van Assche <bvanassche@acm.org>
Date: 2021-04-19 22:17:02
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lkml
On 4/18/21 10:49 PM, Changheun Lee wrote:
quoted hunk ↗ jump to hunk
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@@ -167,6 +168,7 @@ void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_secto max_sectors = round_down(max_sectors, limits->logical_block_size >> SECTOR_SHIFT); limits->max_sectors = max_sectors; + limits->bio_max_bytes = max_sectors << SECTOR_SHIFT; q->backing_dev_info->io_pages = max_sectors >> (PAGE_SHIFT - 9); }Can the new shift operation overflow? If so, how about using check_shl_overflow()?Actually, overflow might be not heppen in case of physical device. But I modified as below. feedback about this.@@ -168,6 +169,9 @@ void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_secto limits->logical_block_size >> SECTOR_SHIFT); limits->max_sectors = max_sectors; + limits->bio_max_bytes = check_shl_overflow(max_sectors, SECTOR_SHIFT, + &limits->bio_max_bytes) ? UINT_MAX : max_sectors << SECTOR_SHIFT; + q->backing_dev_info->io_pages = max_sectors >> (PAGE_SHIFT - 9); } EXPORT_SYMBOL(blk_queue_max_hw_sectors);
If no overflow occurs, check_shl_overflow() stores the result in the
memory location the third argument points at. So the above expression
can be simplified into the following:
if (check_shl_overflow(max_sectors, SECTOR_SHIFT, &limits->bio_max_bytes)) {
limits->bio_max_bytes = UINT_MAX;
}
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diff --git a/include/linux/bio.h b/include/linux/bio.h index d0246c92a6e8..e5add63da3af 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h@@ -106,6 +106,8 @@ static inline void *bio_data(struct bio *bio) return NULL; } +extern unsigned int bio_max_size(struct bio *bio);You may want to define bio_max_size() as an inline function in bio.h such that no additional function calls are introduced in the hot path.I tried, but it is not easy. because request_queue structure of blkdev.h should be referred in bio.h. I think it's not good to apply as a inline function.
Please don't worry about this. Inlining bio_max_size() is not a big concern to me. Thanks, Bart.