From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Date: Fri, 10 Sep 2004 07:45:49 +0000 Subject: Re: Hanging process on SMP machines? Message-Id: <20040910004549.2df18073.akpm@osdl.org> List-Id: References: <20040909201321.GA21492@lucon.org> In-Reply-To: <20040909201321.GA21492@lucon.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: "H. J. Lu" Cc: linux-kernel@vger.kernel.org, linux-ia64@vger.kernel.org "H. J. Lu" wrote: > > I notice that a process may hang on SMP machines at random: > > http://bugzilla.kernel.org/show_bug.cgi?id332 > > I can reliably trigger it within 15 minutes under SMP kernel on P4 HT > and 4-way ia64 machines. Has anyone else seen it? It's easy to reproduce on 2-way x86, however it doesn't look like a kernel bug. akpm 2503 0.0 0.2 3892 640 pts/0 S 00:34 0:00 | \_ make akpm 2504 0.0 0.0 1368 192 pts/0 S 00:34 0:00 | \_ time expect test.exp akpm 2505 0.0 0.5 4776 1276 pts/0 S 00:34 0:00 | \_ expect test.exp akpm 4726 0.0 0.0 0 0 ? Z 00:35 0:00 | \_ [true] process 4726 is sleeping at the end of do_exit(): schedule(); <<- here BUG(); /* Avoid "noreturn function does return". */ for (;;) ; } So it has completely exitted and is waiting for someone to reap its exit code and stack slot via wait4(). So what is its parent up to? (gdb) thread 69 [Switching to thread 69 (Thread 2505)]#0 0xc01653e9 in do_select (n=5, fds=0xcc8b5fa4, timeout=0xcc8b5fa0) at fs/select.c:257 257 __timeout = schedule_timeout(__timeout); (gdb) bt #0 0xc01653e9 in do_select (n=5, fds=0xcc8b5fa4, timeout=0xcc8b5fa0) at fs/select.c:257 #1 0xc016579c in sys_select (n=5, inp=0x804b444, outp=0x804b4c4, exp=0x804b544, tvp=0xbfffe1d0) at fs/select.c:354 #2 0xc0105e39 in sysenter_past_esp () at arch/i386/kernel/semaphore.c:177 The parent is sleeping in select() rather than wait()ing for children. (gdb) f 0 #0 0xc01653e9 in do_select (n=5, fds=0xcc8b5fa4, timeout=0xcc8b5fa0) at fs/select.c:257 257 __timeout = schedule_timeout(__timeout); (gdb) p __timeout $1 = 3000000 For 3,000 seconds. I changed your 3000 to 30 and lo, the script hangs for 30 seconds every now and then, and then resumes.