Bug 140646

Summary: There is an issue with sg_open in RHEL 3.0 U4 .
Product: Red Hat Enterprise Linux 3 Reporter: Heather Conway <conway_heather>
Component: kernelAssignee: Doug Ledford <dledford>
Status: CLOSED NOTABUG QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: 3.0CC: coughlan, digiovanni_lucio, petrides, riel, rkenna
Target Milestone: ---   
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: Bug Fix
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Clone Of: Environment:
Last Closed: 2004-12-03 23:39:38 UTC Type: ---
Regression: --- Mount Type: ---
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Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
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Description Flags
patch to sg_opn for RHEL 3.0 U4 none

Description Heather Conway 2004-11-23 23:43:02 UTC 
From Bugzilla Helper:
User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0; .NET 
CLR 1.0.3705)

Description of problem:
Per the PowerPath team:
The current change to the sg driver in RH3.0 update 4 is buggy and is 
preventing the qualification of PowerPath with update4. 

The issue is in sg_open. When obtaining the request queue spinlock, 
we suggest spin_lock_irq/spin_unlock_irq should be changed to 
spin_lock_irqsave/spin_unlock_irqrestore. Not doing so, improperly 
restores the interrupt mask on the local CPU, and may cause the 
process to be interrupted, when in fact interrupts were disabled by a 
prior spinlock_irq_save on another lock. The result is a deadlock. 

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


How reproducible:
Sometimes

Steps to Reproduce:
The issue is in sg_open. 

Additional info:
Comment 1 Heather Conway 2004-11-23 23:44:13 UTC 
Created attachment 107355 [details]
patch to sg_opn for RHEL 3.0 U4
Comment 3 Doug Ledford 2004-11-26 13:57:18 UTC 
What spin lock is being held while calling sg_open?
Comment 4 Heather Conway 2004-12-02 22:11:38 UTC 
Per the PowerPath team: "A spinlock specific to the Powerpath base 
driver is being held around the call to sg_open."
Does that help or do you need further information?
Thanks.
Comment 5 Doug Ledford 2004-12-03 20:32:02 UTC 
Ugh.  OK, tell them to fix their code.  The sg_open() call is in the
open() syscall chain, is intended for user space use, and is a
function that can sleep.  Holding a spinlock around this is *NOT*
allowed.  The only lock that should ever be held on entry to this
function is the BKL, and that's a lock exception where
sleeping/preemption is allowed.  The use of spin_lock_irq and
unlock_irq is perfectly safe/correct when the function is called
properly.  Calling sg_open with a spin lock held is going to break
horribly on RHEL4 and is broken but we don't spit out BUG()'s on RHEL3.
Comment 6 Heather Conway 2004-12-06 21:34:27 UTC 
Thanks Doug.  I will relay the information to the PowerPath team and 
will let you know if there are any additional questions.
Thanks.
Comment 8 Tom Coughlan 2005-01-28 16:24:43 UTC 
Just in case anyone runs in to this problem: The issue will be fixed
in the next version of PowerPath. EMC is also preparing a hot fix for
the current version if PowerPath.  Contact EMC customer suppport.
Comment 9 Heather Conway 2005-04-08 15:23:37 UTC 
PowerPath 4.3.2 b011 is being released on April 11, 2005.