2013/4/21 James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>: > 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. > Hi. James. > 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: Yes, I agree. And the below patch looks good to fix this issue. Thanks for your comment. > > 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
