LKML Archive on
help / color / mirror / Atom feed
From: Neil Brown <>
To: Al Viro <>
Cc: Andrew Morton <>,,
Subject: Re: [PATCH 002 of 6] md: Fix use-after-free bug when dropping an rdev from an md array.
Date: Mon, 14 Jan 2008 14:21:45 +1100	[thread overview]
Message-ID: <18314.54601.196877.828373@notabene.brown> (raw)
In-Reply-To: message from Al Viro on Monday January 14

On Monday January 14, wrote:
> On Mon, Jan 14, 2008 at 12:45:31PM +1100, NeilBrown wrote:
> > 
> > Due to possible deadlock issues we need to use a schedule work to
> > kobject_del an 'rdev' object from a different thread.
> > 
> > A recent change means that kobject_add no longer gets a refernce, and
> > kobject_del doesn't put a reference.  Consequently, we need to
> > explicitly hold a reference to ensure that the last reference isn't
> > dropped before the scheduled work get a chance to call kobject_del.
> > 
> > Also, rename delayed_delete to md_delayed_delete to that it is more
> > obvious in a stack trace which code is to blame.
> I don't know...  You still get kobject_del() and export_rdev()
> in unpredictable order; sure, it won't be freed under you, but...

I cannot see that that would matter.
kobject_del deletes the object from the kobj tree and free sysfs.
export_rdev disconnects the objects from md structures and releases
the connection with the device.  They are quite independent.

> What is that deadlock problem, anyway?  I don't see anything that
> would look like an obvious candidate in the stuff you are delaying...

Maybe it isn't there any more....

Once upon a time, when I 
   echo remove > /sys/block/mdX/md/dev-YYY/state

sysfs_write_file would hold buffer->sem while calling my store
When my store handler tried to delete the relevant kobject, it would
eventually call orphan_all_buffers which would try to take buf->sem
and deadlock.

orphan_all_buffers doesn't exist any more, so maybe the deadlock is
gone too.
However the comment at the top of sysfs_schedule_callback in
sysfs/file.c says:

 * sysfs attribute methods must not unregister themselves or their parent
 * kobject (which would amount to the same thing).  Attempts to do so will
 * deadlock, since unregistration is mutually exclusive with driver
 * callbacks.

so I'm included to leave the code as it is....  ofcourse the comment
could be well out of date.


  reply	other threads:[~2008-01-14  3:22 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-01-14  1:45 [PATCH 000 of 6] md: various fixes for md NeilBrown
2008-01-14  1:45 ` [PATCH 001 of 6] md: Fix an occasional deadlock in raid5 NeilBrown
2008-01-16  5:01   ` dean gaudet
2008-01-16  5:54     ` Andrew Morton
2008-01-16  6:13       ` dean gaudet
2008-01-16  7:09         ` Dan Williams
2008-01-16  7:15           ` Andrew Morton
2008-01-16 21:54             ` Neil Brown
2008-01-14  1:45 ` [PATCH 002 of 6] md: Fix use-after-free bug when dropping an rdev from an md array NeilBrown
2008-01-14  2:04   ` Al Viro
2008-01-14  3:21     ` Neil Brown [this message]
2008-01-14  3:43       ` Al Viro
2008-01-14  4:48         ` Neil Brown
2008-01-14  6:28           ` Neil Brown
2008-01-14 12:59             ` Al Viro
2008-01-14 13:56               ` Al Viro
2008-01-14  1:45 ` [PATCH 003 of 6] md: Change a few 'int' to 'size_t' in md NeilBrown
2008-01-14  1:45 ` [PATCH 004 of 6] md: Change INTERATE_MDDEV to for_each_mddev NeilBrown
2008-01-14  1:45 ` [PATCH 005 of 6] md: Change ITERATE_RDEV to rdev_for_each NeilBrown
2008-01-14  1:45 ` [PATCH 006 of 6] md: Change ITERATE_RDEV_GENERIC to rdev_for_each_list, and remove ITERATE_RDEV_PENDING NeilBrown

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=18314.54601.196877.828373@notabene.brown \ \ \ \ \ \
    --subject='Re: [PATCH 002 of 6] md: Fix use-after-free bug when dropping an rdev from an md array.' \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).