On Sat, 2013-04-20 at 01:40 +0900, Namjae Jeon wrote: > From: Namjae Jeon <namjae.jeon@xxxxxxxxxxx> > > linux-v3.8-rc1 and later support for plug for blkdev_issue_discard with > commit 0cfbcafcae8b7364b5fa96c2b26ccde7a3a296a9 > (block: add plug for blkdev_issue_discard ) > > For example, > 1) DISCARD rq-1 with size size 4GB > 2) DISCARD rq-2 with size size 1GB > > If these 2 discard requests get merged, final request size will be 5GB. > > In this case, request's __data_len field may overflow as it can store > max 4GB(unsigned int). > > This issue was observed while doing mkfs.f2fs on 5GB SD card: > https://lkml.org/lkml/2013/4/1/292 > > # mkfs.f2fs /dev/mmcblk0p3 > Info: sector size = 512 > Info: total sectors = 11370496 (in 512bytes) > Info: zone aligned segment0 blkaddr: 512 > [ 257.789764] blk_update_request: bio idx 0 >= vcnt 0 > > mkfs process gets stuck in D state and I see the following in the dmesg: > > [ 257.789733] __end_that: dev mmcblk0: type=1, flags=122c8081 > [ 257.789764] sector 4194304, nr/cnr 2981888/4294959104 > [ 257.789764] bio df3840c0, biotail df3848c0, buffer (null), len 1526726656 > [ 257.789764] blk_update_request: bio idx 0 >= vcnt 0 > [ 257.794921] request botched: dev mmcblk0: type=1, flags=122c8081 > [ 257.794921] sector 4194304, nr/cnr 2981888/4294959104 > [ 257.794921] bio df3840c0, biotail df3848c0, buffer (null), len 1526726656 > > Few drivers(e.g. mmc, mtd..) set q->limits.max_discard_sectors > more than UINT_MAX >> 9 sectors which is incorrect and it may lead to overflow > of request's __data_len field if merged discard request's size exceeds 4GB. > > This patchset fixes this issue by updating helper function > blk_queue_max_discard_sectors which is used to set max_discard_sectors limit. > > This patchset also replaces "q->limits.max_discard_sector = max_discard_sectors" > with blk_queue_max_discard_sectors call in other drivers like mmc, mtd etc. I really don't understand this explanation. How can you be affected by the incorrect setting of q->limits.max_discard sectors when n the blkdev_issue_discard() code you see: max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9); ? The problem is not that we issue discards bigger than __data_len can allow, the problem is that we merge them larger than __data_len will allow. That means the merge code needs fixing to pay attention to max_discard_sectors, so isn't this the correct fix: James --- diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 78feda9..33f358f 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -838,7 +838,7 @@ static inline unsigned int blk_queue_get_max_sectors(struct request_queue *q, unsigned int cmd_flags) { if (unlikely(cmd_flags & REQ_DISCARD)) - return q->limits.max_discard_sectors; + return min(q->limits.max_discard_sectors, UINT_MAX >> 9); if (unlikely(cmd_flags & REQ_WRITE_SAME)) return q->limits.max_write_same_sectors; -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
