linux-kernel - 2.6.27.9: splice_to_pipe() hung (blocked for more than 120 seconds)

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Date:	Fri, 16 Jan 2009 19:55:49 +0100
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	lkml <linux-kernel@...r.kernel.org>
Subject: 2.6.27.9: splice_to_pipe() hung (blocked for more than 120 seconds)

Hi,

Seeing some recent splice() discussions, I decided to explore this
system call. I have written a program which might look, well, not very
useful, but the fact is that it creates an unkillable zombie process.
Another funny side effect is that system load continually rises, even
though the system seems to stay fully interactive and functional.

After a while, I also get some messages like this:

Jan 15 20:11:37 localhost kernel: INFO: task a.out:7149 blocked for
more than 120 seconds.
Jan 15 20:11:37 localhost kernel: "echo 0 >
/proc/sys/kernel/hung_task_timeout_secs" disables this message.
Jan 15 20:11:37 localhost kernel: a.out         D ec6e2610     0  7149      1
Jan 15 20:11:37 localhost kernel:       ec5aad44 00000082 c042451f
ec6e2610 00989680 c07da67c c07ddb80 c07ddb80
Jan 15 20:11:37 localhost kernel:       c07ddb80 ec6e4c20 ec6e4e7c
c201db80 00000001 c201db80 470fed45 0000036b
Jan 15 20:11:37 localhost kernel:       ec5aad38 c0421027 ec6e263c
ec6e4e7c ec6e3fa8 85c129f4 ec6e4c20 ec6e4c20
Jan 15 20:11:37 localhost kernel: Call Trace:
Jan 15 20:11:37 localhost kernel: [<c064420f>] __mutex_lock_common+0x8a/0xd9
Jan 15 20:11:37 localhost kernel: [<c0644302>] __mutex_lock_slowpath+0x12/0x15
Jan 15 20:11:37 localhost kernel: [<c0644181>] mutex_lock+0x29/0x2d
Jan 15 20:11:37 localhost kernel: [<c04aa8f1>] splice_to_pipe+0x23/0x1f5
Jan 15 20:11:37 localhost kernel: [<c04ab290>]
__generic_file_splice_read+0x3ff/0x413
Jan 15 20:11:37 localhost kernel: [<c04ab324>]
generic_file_splice_read+0x80/0x9a
Jan 15 20:11:37 localhost kernel: [<c04a9e95>] do_splice_to+0x4e/0x5f
Jan 15 20:11:37 localhost kernel: [<c04aa010>] sys_splice+0x16a/0x1c8
Jan 15 20:11:37 localhost kernel: [<c0403cca>] syscall_call+0x7/0xb
Jan 15 20:11:37 localhost kernel: =======================

(but this was from such a system with 6 zombies and ~80 load. See
attachments for SysRq report with processes in blocked state, it has
similar info but for just one zombie.)

This happens with 2.6.27.9-73.fc9.i686 kernel. Maybe it was fixed
recently? (In any case, I don't think it is a regression.)

It seems to be not 100% reproducible. Sometimes it works, sometimes
not. Start the program, then after a while hit Ctrl-C. If it doesn't
exit, zombie count will rise and system state will be as described.
Compile with -lpthread.

Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036

View attachment "socket-pipe.c" of type "text/x-csrc" (2125 bytes)

View attachment "splice-hang.txt" of type "text/plain" (11312 bytes)