Re: [2.6.18-rc2-gabb5a5cc BUG] Lukewarm IQ detected in hotplug locking

From: Michal Piotrowski
Date: Wed Jul 26 2006 - 04:49:28 EST

On 26/07/06, Paul Jackson <pj@xxxxxxx> wrote:
Michal - you addressed this to me. This isn't my area.

I was wrong, sorry.

Hopefully someone else can handle this. Good luck.

Here is the bad commit

aa95387774039096c11803c04011f1aa42d85758 is first bad commit
commit aa95387774039096c11803c04011f1aa42d85758
Author: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxx>
Date: Sun Jul 23 12:12:16 2006 -0700

cpu hotplug: simplify and hopefully fix locking

The CPU hotplug locking was quite messy, with a recursive lock to
handle the fact that both the actual up/down sequence wanted to
protect itself from being re-entered, but the callbacks that it
called also tended to want to protect themselves from CPU events.

This splits the lock into two (one to serialize the whole hotplug
sequence, the other to protect against the CPU present bitmaps
changing). The latter still allows recursive usage because some
subsystems (ondemand policy for cpufreq at least) had already gotten
too used to the lax locking, but the locking mistakes are hopefully
now less fundamental, and we now warn about recursive lock usage
when we see it, in the hope that it can be fixed.

Signed-off-by: Linus Torvalds <torvalds@xxxxxxxx>

:040000 040000 9189d56fe28f6823287e9d1e79976e68074da5db
4ba2c4f332c7c0ce M include
:040000 040000 3dfe69afef86aef8e6472d6d543ba965833e201b
2526fd11b789d51e M kernel

I won't rest till it's the best ...
Programmer, Linux Scalability
Paul Jackson <pj@xxxxxxx> 1.925.600.0401


Michal K. K. Piotrowski
LTG - Linux Testers Group
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