From a8733c7baf457b071528e385a0b7d4aaec79287c Mon Sep 17 00:00:00 2001 From: James Bottomley Date: Fri, 17 Dec 2010 15:36:34 -0500 Subject: [SCSI] fix medium error problems with some arrays which can cause data corruption Our current handling of medium error assumes that data is returned up to the bad sector. This assumption holds good for all disk devices, all DIF arrays and most ordinary arrays. However, an LSI array engine was recently discovered which reports a medium error without returning any data. This means that when we report good data up to the medium error, we've reported junk originally in the buffer as good. Worse, if the read consists of requested data plus a readahead, and the error occurs in readahead, we'll just strip off the readahead and report junk up to userspace as good data with no error. The fix for this is to have the error position computation take into account the amount of data returned by the driver using the scsi residual data. Unfortunately, not every driver fills in this data, but for those who don't, it's set to zero, which means we'll think a full set of data was transferred and the behaviour will be identical to the prior behaviour of the code (believe the buffer up to the error sector). All modern drivers seem to set the residual, so that should fix up the LSI failure/corruption case. Reported-by: Douglas Gilbert Cc: Stable Tree Signed-off-by: James Bottomley --- drivers/scsi/sd.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) (limited to 'drivers/scsi') diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c index d8e2caf9f468..365024b0c407 100644 --- a/drivers/scsi/sd.c +++ b/drivers/scsi/sd.c @@ -1188,6 +1188,12 @@ static unsigned int sd_completed_bytes(struct scsi_cmnd *scmd) u64 end_lba = blk_rq_pos(scmd->request) + (scsi_bufflen(scmd) / 512); u64 bad_lba; int info_valid; + /* + * resid is optional but mostly filled in. When it's unused, + * its value is zero, so we assume the whole buffer transferred + */ + unsigned int transferred = scsi_bufflen(scmd) - scsi_get_resid(scmd); + unsigned int good_bytes; if (scmd->request->cmd_type != REQ_TYPE_FS) return 0; @@ -1221,7 +1227,8 @@ static unsigned int sd_completed_bytes(struct scsi_cmnd *scmd) /* This computation should always be done in terms of * the resolution of the device's medium. */ - return (bad_lba - start_lba) * scmd->device->sector_size; + good_bytes = (bad_lba - start_lba) * scmd->device->sector_size; + return min(good_bytes, transferred); } /** -- cgit v1.2.3-70-g09d2