blk-mq: fix undefined behaviour in order_to_size()
When this_order variable in blk_mq_init_rq_map() becomes zero
the code incorrectly decrements the variable and passes the result
to order_to_size() helper causing undefined behaviour:
UBSAN: Undefined behaviour in block/blk-mq.c:1459:27
shift exponent 4294967295 is too large for 32-bit type 'unsigned int'
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.6.0-rc6-00072-g33656a1 #22
Fix the code by checking this_order variable for not having the zero
value first.
Reported-by: Meelis Roos <mroos@linux.ee>
Fixes: 320ae51fee
("blk-mq: new multi-queue block IO queueing mechanism")
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
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@ -1495,7 +1495,7 @@ static struct blk_mq_tags *blk_mq_init_rq_map(struct blk_mq_tag_set *set,
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int to_do;
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void *p;
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while (left < order_to_size(this_order - 1) && this_order)
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while (this_order && left < order_to_size(this_order - 1))
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this_order--;
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do {
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