Bug 64149 - Bug in scsi_merge.c
Summary: Bug in scsi_merge.c
Alias: None
Product: Red Hat Linux
Classification: Retired
Component: kernel (Show other bugs)
(Show other bugs)
Version: 7.2
Hardware: i386 Linux
Target Milestone: ---
Assignee: Doug Ledford
QA Contact: Brian Brock
Depends On:
TreeView+ depends on / blocked
Reported: 2002-04-26 16:55 UTC by Tom "spot" Callaway
Modified: 2007-04-18 16:42 UTC (History)
5 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
Last Closed: 2003-02-13 18:20:33 UTC
Type: ---
Regression: ---
Mount Type: ---
Documentation: ---
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

Attachments (Terms of Use)
scsi_merge.c patch (337 bytes, patch)
2002-04-26 16:56 UTC, Tom "spot" Callaway
no flags Details | Diff

External Trackers
Tracker ID Priority Status Summary Last Updated
Red Hat Product Errata RHSA-2002:227 high SHIPPED_LIVE Important: kernel security update 2002-10-08 04:00:00 UTC

Description Tom "spot" Callaway 2002-04-26 16:55:57 UTC
filing on behalf of Ed Goggin @ EMC

Description of Problem:

The bug is in __init_io() of drivers/scsi/scsi_merge.c.
This bug causes partially completed i/os (special requests)
to occur in cases where an i/o request consists of only a
single segment but multiple buffer headers.  This will only
happen with an HBA driver which supports DMA clustering.  We
get hundreds if not thousands of such partially completed i/os
to occur by issuing either raw or buffered sd device i/o.

The major effect of this bug is to slow down i/o throughput
since the linux scsi subsystem appears to handle such partially
completed i/os by re-issuing the residual portion of the i/o
as a special request.

Version-Release number of selected component (if applicable):


The patch for this is simple (1 liner) and is attached to this bugreport.

Comment 1 Tom "spot" Callaway 2002-04-26 16:56:30 UTC
Created attachment 55484 [details]
scsi_merge.c patch

Comment 2 Matt Domsch 2002-07-02 15:13:57 UTC
This is addressed in a separate fix in the 2.4.19-rc1 kernel at least (I don't 
know when it was added exactly):

         * Don't bother with scatter-gather if there is only one segment.
        if (count == 1) {
                this_count = SCpnt->request.nr_sectors;
                goto single_segment;
The incorrect code is present in 2.4.18-3 at least.

Comment 3 Matt Domsch 2002-07-02 16:49:43 UTC
Dell and EMC would like to see this fixed in a Pensacola errata kernel.

Comment 4 Gary Lerhaupt 2002-07-19 20:09:04 UTC
Kyu (ykang@redhat.com) informed us that the patch included in this bugzilla 
will be added to the next AS errata.  Can this be confirmed?

Comment 5 Yil-Kyu Kang 2002-07-19 20:52:22 UTC
Yes, this patch has been accepted and we are planning on shipping this in our
next AS errata.

Comment 6 Tom Coughlan 2002-09-20 20:10:54 UTC
This fix is checked in to the AS CVS source tree.  We expect it to ship in an
errata as soon feasible.

Comment 7 Matt Domsch 2003-02-13 18:20:33 UTC
Fixed in kernel 2.4.9-e.9 at least, and 2.4.20-based kernels slated for 
GinGin.  Closing.

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