Re: [Patch mdadm] Add hot-unplug support to mdadm

[Doug Ledford <dledford@redhat.com>]

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On 04/13/2010 05:28 AM, Tomáš Dulík wrote:
> Hi Doug,
> 
> first of all: thanks for your work on hot-unplug!
> I am new to Linux RAID, have been using HW RAID before but after my LSI
> controller burned to ashes I decided I don't want to see HW RAID ... ever.
> 
> First thing I found weird on Linux RAID was the missing support for dead
> device removal.
> I spent last 3 weeks trying to write various scripts for UDEV "remove"
> and mdadm "Fail" events handling, but finally I found the same thing
> like you - it is not possible to remove dead device from an array,
> because the events are issued too late. The only way to remove dead
> device is reboot, which is not what I would expect as solution in Linux
> world.
> 
> So I downloaded your code from Neil's git
> (http://neil.brown.name/git?p=mdadm;a=shortlog;h=refs/heads/hotunplug)
> and also applied the "Minor incremental fixup" mentioned in your message
> below.
> 
> The compiled mdadm works OK for normal operations (--fail, --remove,
> --add), but crashes with Segmentation fault for the "--incremental
> --fail" operation if I use it for a disk that I have just disconnected.
> Here is what I've got:
> 
> # gdb --args ./mdadm -If sda3
> GNU gdb 6.8-debian
> This GDB was configured as "x86_64-linux-gnu"...
> (gdb) run
> Starting program: /root/mdadm-git/mdadm/mdadm -If sda3
> Program received signal SIGSEGV, Segmentation fault.
> 0x000000000040a796 in mdstat_by_component (name=0x7fff0d0aee83 "sda3")
> at mdstat.c:351
> 351                     if (ent->metadata_version &&
> (gdb) where
> #0  0x000000000040a796 in mdstat_by_component (name=0x7fff0d0aee83
> "sda3") at mdstat.c:351
> #1  0x000000000042411c in IncrementalRemove (devname=0x7fff0d0aee83
> "sda3", verbose=0) at Incremental.c:867
> #2  0x00000000004075a7 in main (argc=3, argv=0x7fff0d0ad698) at
> mdadm.c:1545
> 
> It does not matter if I use sda3 or sda, the result is the same.
> What am I doing wrong?

There was a thinko in Neil's patch that is fixed with the attached patch.

-- 
Doug Ledford <dledford@redhat.com>
              GPG KeyID: CFBFF194
	      http://people.redhat.com/dledford

Infiniband specific RPMs available at
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From b937950110190ce00f16d91a3423a66fde080a95 Mon Sep 17 00:00:00 2001
From: Doug Ledford <dledford@redhat.com>
Date: Tue, 13 Apr 2010 13:12:59 -0400
Subject: [PATCH 1/4] [hotunplug] we are testing mdstat, not ent which is undefined at this
 point

Signed-off-by: Doug Ledford <dledford@redhat.com>
---
 mdstat.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/mdstat.c b/mdstat.c
index 58d349d..3bb74fa 100644
--- a/mdstat.c
+++ b/mdstat.c
@@ -348,9 +348,9 @@ struct mdstat_ent *mdstat_by_component(char *name)
 	while (mdstat) {
 		struct dev_member *m;
 		struct mdstat_ent *ent;
-		if (ent->metadata_version &&
-		    strncmp(ent->metadata_version, "external:", 9) == 0	 &&
-		    is_subarray(ent->metadata_version+9))
+		if (mdstat->metadata_version &&
+		    strncmp(mdstat->metadata_version, "external:", 9) == 0 &&
+		    is_subarray(mdstat->metadata_version+9))
 			/* don't return subarrays, only containers */
 			;
 		else for (m = mdstat->members; m; m = m->next) {
-- 
1.6.6.1


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