linux-kernel - Re: [bug] ata subsystem related crash with latest -git

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Message-ID: <20071018091706.GO5063@kernel.dk>
Date:	Thu, 18 Oct 2007 11:17:06 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [bug] ata subsystem related crash with latest -git

On Thu, Oct 18 2007, Jeff Garzik wrote:
> Jens Axboe wrote:
>> index 4df8311..b858183 100644
>> --- a/drivers/ata/sata_mv.c
>> +++ b/drivers/ata/sata_mv.c
>> @@ -1139,6 +1139,7 @@ static void mv_fill_sg(struct ata_queued_cmd *qc)
>>  	struct mv_port_priv *pp = qc->ap->private_data;
>>  	struct scatterlist *sg;
>>  	struct mv_sg *mv_sg;
>> +	int end_marked = 0;
>>   	mv_sg = pp->sg_tbl;
>>  	ata_for_each_sg(sg, qc) {
>> @@ -1159,13 +1160,15 @@ static void mv_fill_sg(struct ata_queued_cmd *qc)
>>  			sg_len -= len;
>>  			addr += len;
>>  -			if (!sg_len && ata_sg_is_last(sg, qc))
>> +			if (!sg_len && ata_sg_is_last(sg, qc)) {
>>  				mv_sg->flags_size |= cpu_to_le32(EPRD_FLAG_END_OF_TBL);
>> +				end_marked++;
>> +			}
>>   			mv_sg++;
>>  		}
>> -
>>  	}
>> +	BUG_ON(end_marked != 1);
>
>
> Your BUG_ON() does indeed trip, here.
>
> Its surprising that other folks don't explode, considering that 
> mv_fill_sg() intentionally mirrors the logic in ata_fill_sg().

The sata_mv construct looks a bit odd. Does this work? That last
end_mv_sg test should always be true, just being paranoid...

diff --git a/drivers/ata/sata_mv.c b/drivers/ata/sata_mv.c
index 4df8311..5397eea 100644
--- a/drivers/ata/sata_mv.c
+++ b/drivers/ata/sata_mv.c
@@ -1138,8 +1138,9 @@ static void mv_fill_sg(struct ata_queued_cmd *qc)
 {
 	struct mv_port_priv *pp = qc->ap->private_data;
 	struct scatterlist *sg;
-	struct mv_sg *mv_sg;
+	struct mv_sg *mv_sg, *end_mv_sg;
 
+	end_mv_sg = NULL;
 	mv_sg = pp->sg_tbl;
 	ata_for_each_sg(sg, qc) {
 		dma_addr_t addr = sg_dma_address(sg);
@@ -1158,14 +1159,12 @@ static void mv_fill_sg(struct ata_queued_cmd *qc)
 
 			sg_len -= len;
 			addr += len;
-
-			if (!sg_len && ata_sg_is_last(sg, qc))
-				mv_sg->flags_size |= cpu_to_le32(EPRD_FLAG_END_OF_TBL);
-
+			end_mv_sg = mv_sg;
 			mv_sg++;
 		}
-
 	}
+	if (end_mv_sg)
+		end_mv_sg->flags_size |= cpu_to_le32(EPRD_FLAG_END_OF_TBL);
 }
 
 static inline void mv_crqb_pack_cmd(__le16 *cmdw, u8 data, u8 addr, unsigned last)

-- 
Jens Axboe

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