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From: "Canham, Timothy K (348C)" <timothy.k.canham@jpl.nasa.gov>
To: "cygwin@cygwin.com" <cygwin@cygwin.com>
Subject: RE: pthread_attr_init() returning errors
Date: Wed, 20 Apr 2016 14:20:25 +0000
Message-ID: <E8EB3633A6A4594CA063A3FCBC82C18C3621FDE3@ap-embx-sp40.RES.AD.JPL>
References: <E8EB3633A6A4594CA063A3FCBC82C18C3621F0F6@ap-embx-sp40.RES.AD.JPL> <20160420105016.GB26118@calimero.vinschen.de>
In-Reply-To: <20160420105016.GB26118@calimero.vinschen.de>
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So what you are saying is that when pthread_attr_init() checked for the magic number in supposedly uninitialized memory it found the exact value of the magic number? That seems highly suspect. Seems like it may be pointing to a valid previous entry.

Tim Canham
JPL Flight Software


-----Original Message-----
From: Corinna Vinschen [mailto:corinna-cygwin@cygwin.com] 
Sent: Wednesday, April 20, 2016 3:50 AM
To: cygwin@cygwin.com
Cc: Canham, Timothy K (348C) <timothy.k.canham@jpl.nasa.gov>
Subject: Re: pthread_attr_init() returning errors

On Apr 19 19:49, Canham, Timothy K (348C) wrote:
> I have some code to start a task that suddenly started failing. This 
> is pretty mature code. Here is the code fragment with my added 
> printf()
> 
>         pthread_attr_t att;
>         int stat = pthread_attr_init(&att);
>         if (stat != 0) {
>             printf("pthread_attr_init: (%d)(%d): %s\n",stat,errno,strerror(stat));
>             // return
>         }
> 
> Here is the output:
> 
> pthread_attr_init: (16)(0): Device or resource busy

This is most unusual.  What happens is this:

A pthread_attr_t is a pointer to a pointer to a struct with a magic number.  And at the start of pthread_attr_init this magic number is tested if it's already the magic number expected for an object of type pthread_attr_t.  And only if so, the pthread_attr_init function fails with EBUSY.

That means, the arbitrary value in the uninitialized att prior to the call to pthread_attr_init is a pointer value which points to valid memory which has the magic value 0xdf0df048.  Wow.

This means we can't keep up with the tests in the pthread_FOO_init functions since they could point to an *supposedly* initialized object, while in fact the value they point to is only accidentally so that it looks like an initialized object.

I provided new developer snapshots on https://cygwin.com/snapshots/ and I've just uploaded a 2.5.1-0.1 test release which you can install via setup as soon as your mirror has catched up.

Pleaser give any of them a try.


Thanks,
Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat