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Date: Sat, 30 Mar 2013 18:05:45 +0530 From: Vineet Gupta <Vineet.Gupta1@...opsys.com> To: lkml <linux-kernel@...r.kernel.org>, <linux-serial@...r.kernel.org> CC: Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Jiri Slaby <jslaby@...e.cz>, Peter Hurley <peter@...leysoftware.com> Subject: n_tty_write() going into schedule but NOT coming out Hi, I've been stress testing ARC Linux 3.8 (same happens for 3.9-rc3 as well). The setup has 3 telnet sessions, each running find . -name "*" in a loop. The platform is a FPGA @ 80 MHz, running a single core ARC700 so kernel .config has !SMP and PREEMPT_NONE. After ~10 mins of run, I see that one of the telnet session gets stuck (and later the 2nd one as well), while system is still alive, 3rd telnet is running find merrily. [ARCLinux]$ ps .... 7 root 0:00 inetd 62 root 0:00 -/bin/sh 64 root 1:34 telnetd -i -l /bin/sh 65 root 0:00 /bin/sh 75 root 1:47 telnetd -i -l /bin/sh 76 root 0:00 /bin/sh 79 root 0:53 telnetd -i -l /bin/sh 80 root 0:00 /bin/sh 281 root 0:00 find / -name * <--- stuck 358 root 0:03 find / -name * <--- stuck 377 root 0:00 find / -name * 378 root 0:00 ps Hung find task is sitting in the schedule() call in n_tty_write() [ARCLinux]$ cat /proc/281/stack [<8065945e>] n_tty_write+0x23a/0x424 [<80655cd4>] tty_write+0x1ac/0x2d4 [<805976ba>] vfs_write+0x92/0x110 [<80597816>] sys_write+0x4e/0x88 [<8050e780>] ret_from_system_call+0x0/0x4 This task never resumes out of schedule() - verified by putting a hardware breakpoint on next insn - using a JTAG host debugger. Attached are .config, /proc/281/sched, /proc/schedstat, /proc/sched_debug My knowledge of schedular is close to none, hence any tips to debug this further would be much appreciated. TIA, -Vineet View attachment ".config" of type "text/plain" (21892 bytes) View attachment "proc_pid_sched.log" of type "text/x-log" (2365 bytes) View attachment "proc_sched_debug.log" of type "text/x-log" (2577 bytes) View attachment "proc_schedstat.log" of type "text/x-log" (96 bytes)
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