Re: [PATCH v2] rt2x00: rt2800usb: fix races in tx queue

[Stanislaw Gruszka <sgruszka@redhat.com>]

On Tue, Aug 09, 2011 at 05:45:40PM +0200, Stanislaw Gruszka wrote:
> On Tue, Aug 09, 2011 at 01:26:24PM +0200, Stanislaw Gruszka wrote:
> > > > Second, I think it would be appropriate to split the patch in 2, or maybe 3, parts:
> > > > 	1. The hunk to rt2x00usb to reverse the entry flag handling and the tx dma done handling.
> > > > 	2. The hunk that checks that the entry on which the TX status is being reported has
> > > >            already been properly completed its TX done handling.
> > > > 	3. The remainder, i.e. the retrying of handling a TX status report if the entry hasn't been
> > > >            fully completed its TX done handling yet. 
> > > > 
> > > > The code in this area has been proven to be very fragile, so I prefer to make mini changes to it in
> > > > small steps, so that we can properly bisect which change exactly has caused a problem.
> > > > 
> > > > See further down for more thoughts.
> > > 
> > > Thanks for comments. I'll repost small patch that should fix the bug
> > > and don't do things you dislike.
> > 
> > Hmm, I planed to post the below patch, but unfortunately it does not fix
> > the crash on my system (rare reproducible after an hour of working). Seems
> > there are more problems here. Looks like there is possibility to mishmash
> > indexes i.e. make indexes like {Q_INDEX, Q_INDEX_DMA_DONE, Q_INDEX_DONE}
> > = {44, 54, 44}, whereas they should be {44, 44, 44} or {45, 43, 41}. 
> > Original patch seems to preventing this (fix or mask the problem), but 
> > honestly I do not understand way. I have to look more closely at it.
> 
> Ok, I think I found these other problems, seems we have also check 
> ENTRY_DATA_PENDING flags and add similar checks in rt2800usb_work_txdone
> when checking against failed I/O.
> 
> Justin, if you have opportunity test below patch (for 3.0 kernel). It does
> not crash here so far, but on my system bug is very rarely reproducible,
> so I have to test whole night or more to be sure.
> 
> Comments welcome. If patch is ok, I will split it into 2 parts and post
> officially.

This patch crashes as well. I have to debug this issue a bit more ...

Stanislaw