netdev - Re: [4.14rc6] __tcp_select

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Date:   Fri, 3 Nov 2017 09:37:28 -0400
From:   Dave Jones <davej@...emonkey.org.uk>
To:     netdev@...r.kernel.org
Subject: Re: [4.14rc6] __tcp_select_window divide by zero.

On Tue, Oct 24, 2017 at 09:00:30AM -0400, Dave Jones wrote:
 > divide error: 0000 [#1] SMP KASAN
 > CPU: 0 PID: 31140 Comm: trinity-c12 Not tainted 4.14.0-rc6-think+ #1 
 > RIP: 0010:__tcp_select_window+0x21f/0x400
 > Call Trace:
 >  tcp_cleanup_rbuf+0x27d/0x2a0
 >  tcp_recvmsg+0x7a9/0x1430
 >  inet_recvmsg+0x10b/0x360
 >  sock_read_iter+0x19d/0x240
 >  do_iter_readv_writev+0x2e4/0x320
 >  do_iter_read+0x149/0x280
 >  vfs_readv+0x107/0x180
 >  do_readv+0xc0/0x1b0
 >  do_syscall_64+0x182/0x400
 >  entry_SYSCALL64_slow_path+0x25/0x25
 > Code: 41 5e 41 5f c3 48 8d bb 48 09 00 00 e8 4b 2b 30 ff 8b 83 48 09 00 00 89 ea 44 29 f2 39 c2 7d 08 39 c5 0f 8d 86 01 00 00 89 e8 99 <41> f7 fe 89 e8 29 d0 eb 8c 41 f7 df 48 89 c7 44 89 f9 d3 fd e8 
 > RIP: __tcp_select_window+0x21f/0x400 RSP: ffff8803df54f418
 > 
 >
 >                if (window <= free_space - mss || window > free_space)
 >                        window = rounddown(free_space, mss);

I'm still hitting this fairly often, so I threw in a debug patch, and
when this happens..

[53182.361210] window: 0 free_space: 0 mss: 0

Any suggestions on what we should default the window size to be in
this situation to avoid the rounddown ?


	Dave