Re: Observed deadlock in ext4 under 3.2.23-rt37 & 3.2.33-rt50

[Theodore Ts'o <tytso@mit.edu>]

On Thu, Jan 03, 2013 at 08:36:39AM -0600, Staffan Tjernstrom wrote:
> This may be completely off-in-newbie land, but I figured I'd throw in what I think I've tracked down.
> 
> It looks as if there was a fairly recent patch to turn locks in
> parts of the code into atomic instructions (apologies - I don't have
> the patch id to hand atm) in do_get_write_access() amongst others.

In fs/jbd2/transaction.c?  Can you give me the code snippit and/or
function and line number that you're concerned about?

> Then in turn the C++ standard library loops around calls to write()
> whilst access isn't available, basically blocking on the atomic
> (which then in turn doesn't support priority inheritance), causing
> the wait loop.

Yeah, but do_get_write_access() blocks (usually waiting for the jbd2
kernel thread to complete, but possibly on a memory allocation); we
don't return EAGAIN or anything like that.  So I don't see how that
would cause a wait loop.

It's possible we could be returning -ENOMEM; are you looping for all
write failures, or just for EAGAIN/EINTR and partial writes?

	      	     	  	    - Ted