lkml.org 
[lkml]   [2000]   [Oct]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
Subjecttcp.c::wait_for_tcp_memory() buggy ?
Hi Davem,

I can't quite put my finger on what wait_for_tcp_memory() is
supposed to do, but the code looks EXTREMELY suspect and I've
had a report of somebody looping in the for(;;) loop in that
function without ever exiting and getting his TCP connection
stuck there...

Also, the locking inside the loop seems fragile, to say the
least.

from tcp.c:

865 if (tcp_memory_free(sk) && !vm_wait)
866 break;

880 release_sock(sk);
881 if (!tcp_memory_free(sk) || vm_wait)
882 current_timeo = schedule_timeout(current_timeo);
883 lock_sock(sk);

Here we hold the lock for the entire loop (meaning that
other people cannot make the exit condition on line 865
come true.

Except for doing a test on tcp_memory_free(sk), where we
do NOT hold the lock we're so dutifully clinging to during
the rest of the loop...

As I said, I can't put my finger down on what exactly is
wrong, but this code looks subtle enough that, together
with the bugreport I got (on IRC), I have the feeling that
it just _can't_ be right ...

regards,

Rik
--
"What you're running that piece of shit Gnome?!?!"
-- Miguel de Icaza, UKUUG 2000

http://www.conectiva.com/ http://www.surriel.com/

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 12:45    [W:0.129 / U:0.304 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site