Re: 2.6.38.x: system hangs, iowait ~75, no resource-hogs, no logs

[Kelly Anderson <kelly@silka.with-linux.com>]

On 04/07/11 16:21, Thomas Sattler wrote:
> Hi there ...
>
> I observed three system hangs since 2.6.38 (two times 2.6.38,
> once 2.6.38.2). I have no idea what triggers the problem, I
> cannot find the cause myself. I tried these:
>
> top:
> ~~~~
>   - no cpu-hogg, still a bit free RAM, lots of free SWAP
>   - iowait is constantly high at ~75%, I don't know why
>
> dmesg, /var/log/*:
> ~~~~~~~~~~~~~~~~~~
> Nothing in 'dmesg', nothing in the logfiles.
>
> pkill / iotop / ps:
> ~~~~~~~~~~~~~~~~~~~
> they all hang quite soon, no reaction on Ctrl-C. While 'ps'
> shows some lines of output, 'pkill' and 'iotop' just hang.
>
> vmstat 1:
> ~~~~~~~~~
> procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
>   r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
>   0  4     72 421008  54560 326652    0    0     0     0  518 1293 25  9  0 66
>   0  4     72 421008  54560 326652    0    0     0     0  311  535 13  4  0 83
>   2  4     72 420208  54560 326652    0    0     0     0  450  882 18  9  0 73
>   0  4     72 421008  54560 326652    0    0     0     0  377  914 19  5  0 76
> (I collected about 90 lines, there's not much to be seen.)
>
> I run 'strace -o dump command' with iotop, ps and su.
> (And lost a tty to each of them.)
>
> $ tail dump_*
> ==>  dump_iotop<==
> fstat64(9, {st_mode=S_IFREG|0644, st_size=2952, ...}) = 0
> mmap2(NULL, 2952, PROT_READ, MAP_SHARED, 9, 0) = 0xb6d80000
> _llseek(9, 2952, [2952], SEEK_SET)      = 0
> munmap(0xb6d80000, 2952)                = 0
> close(9)                                = 0
> open("/proc/5904/cmdline", O_RDONLY|O_LARGEFILE) = 9
> fstat64(9, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
> fstat64(9, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
> 0xb6d80000
> read(9,
> ==>  dump_ps<==
> stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2309, ...}) = 0
> stat64("/proc/5904", {st_mode=S_IFDIR|0555, st_size=0, ...}) = 0
> open("/proc/5904/stat", O_RDONLY)       = 6
> read(6, "5904 (thunderbird-bin) D 5900 58"..., 1023) = 242
> close(6)                                = 0
> open("/proc/5904/status", O_RDONLY)     = 6
> read(6, "Name:\tthunderbird-bin\nState:\tD ("..., 1023) = 836
> close(6)                                = 0
> open("/proc/5904/cmdline", O_RDONLY)    = 6
> read(6,
> ==>  dump_su<==
> stat64("/home/tsattler/.pam_environment", 0xbffdb3e0) = -1 ENOENT (No such
> file or directory)
> access("/usr/bin/xauth", X_OK)          = 0
> setuid32(1000)                          = 0
> chdir("/home/tsattler")                 = 0
> close(3)                                = 0
> clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
> child_tidptr=0xb75f3728) = 25247
> rt_sigprocmask(SIG_BLOCK, ~[RTMIN RT_1], NULL, 8) = 0
> rt_sigaction(SIGTERM, {0x8049ce0, [], 0}, NULL, 8) = 0
> rt_sigprocmask(SIG_UNBLOCK, [ALRM TERM], NULL, 8) = 0
> waitpid(-1,
>
> 'top' showed constantly increasing sysload, I rebooted
> (via Alt-SysRq-[S][U][B]) at a load of about 25-30.
>
> My system is as follows:
> ~~~~~~~~~~~~~~~~~~~~~~~~
> IBM T41p, 1.5GB RAM, 4GB SWAP (nearly unused), two HDs
> 160/80GB. Gentoo Linux, kernel 2.6.38.2 (vanilla sources).
>
> I compiled the kernel myself. I skipped 2.6.37 but run
> 2.6.36.3 with sabayon's fourth version of a backport of
> sched-automated-per-session-task-groups.patch for more
> than two months without any problems.
>
> CPU-Speed is 1700MHz (hardware) but I run the machine
> at 1400MHz most of the time as the fans become loud
> when running at full speed.
>
> ** Please CC: me, as I'm not on the list. **
>
> Thomas
>
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Try the patch found in "Linux 2.6.38 freeze because of 
sound/core/pcm_lib.c commit"