Re: ps hang in 241-pre10

[Marcelo Tosatti]

On Sat, 27 Jan 2001, Linus Torvalds wrote:

> 
> 
> On Sun, 28 Jan 2001, Marcelo Tosatti wrote:
> > > 
> > > This is the smoking gun here, I bet, but I'd like to make sure I see the
> > > whole thing. I don't see _why_ we'd have deadlocked on __wait_on_page(),
> > > but I think this is the thread that hangs on to the mm semaphore.
> > 
> > I was able to reproduce it here with dbench. 
> > 
> > Nothing is locked except this dbench thread (the only dbench thread):
> > 
> > dbench    D C1C9FE64  5200  1013      1        (L-TLB)    1370   785 
> > Call Trace: [___wait_on_page+130/160] [truncate_list_pages+100/404] [truncate_inode_pages+93/128] [iput+162/360] [dput+262/356] [fput+121/232] [exit_mmap+218/292]  
> > [mmput+56/80] [do_exit+208/680] [do_signal+566/656] [dput+25/356] [path_release+13/60] [sys_newstat+100/112] [sys_read+188/196] [signal_return+20/24]  
> 
> Ok, this definitely seems to be the pattern.
> 
> I don't see _what_ is going on, though.
> 
> I know of one "known bug" in pre10: if you run out of swap-space with
> shared memory segments, it will do the wrong thing (return 1 without
> unlocking the page). xmms might trigger this, but I didn't think that
> dbench used shared memory?

It does. Bingo.

I'm not able to reproduce the problem here with your patch. 

Btw, there is another bug in shm_writepage() where it does not set the
page dirty in case of failure...