Re: 2.6.35-rc3 deadlocks on semaphore operations

[Manfred Spraul <manfred@colorfullife.com>]

Hi Luca,

On 06/26/2010 02:52 PM, Luca Tettamanti wrote:
> They don't seem really hung as before, I see two different behaviours:
> * Near the end of the run ab is frozen for a few seconds, but in the
> end all requests are processed; however I see a few "length" errors,
> meaning that the received page does not match the expected content
> (I'm testing a static page):
>
> Concurrency Level:      100
> Time taken for tests:   14.682 seconds
> Complete requests:      10000
> Failed requests:        10
>     (Connect: 0, Receive: 0, Length: 10, Exceptions: 0)
> Write errors:           0
> Total transferred:      79987946 bytes
> HTML transferred:       77190466 bytes
> Requests per second:    681.11 [#/sec] (mean)
> Time per request:       146.819 [ms] (mean)
> Time per request:       1.468 [ms] (mean, across all concurrent requests)
> Transfer rate:          5320.36 [Kbytes/sec] received
>
> Connection Times (ms)
>                min  mean[+/-sd] median   max
> Connect:        0    1   0.4      0       3
> Processing:     3   29 428.9     15   14678
> Waiting:        0   15   1.3     15      19
> Total:          5   30 429.0     16   14682
> ERROR: The median and mean for the initial connection time are more
> than twice the standard
>         deviation apart. These results are NOT reliable.
> Percentage of the requests served within a certain time (ms)
>    50%     16
>    66%     17
>    75%     17
>    80%     17
>    90%     17
>    95%     17
>    98%     18
>    99%     18
>   100%  14682 (longest request)
>
> strace on apache shows:
> [pid  3787] restart_syscall(<... resuming interrupted call ...>  <unfinished ...>
> [pid  3789] restart_syscall(<... resuming interrupted call ...>  <unfinished ...>
> [pid  3788] restart_syscall(<... resuming interrupted call ...>  <unfinished ...>
> [pid  3784] restart_syscall(<... resuming interrupted call ...>  <unfinished ...>
> [pid  3783] restart_syscall(<... resuming interrupted call ...>  <unfinished ...>
> [pid  3782] restart_syscall(<... resuming interrupted call ...>  <unfinished ...>
> [pid  3239] restart_syscall(<... resuming interrupted call ...>  <unfinished ...>
> [pid  3233] restart_syscall(<... resuming interrupted call ...>  <unfinished ...>
> [pid  3238] restart_syscall(<... resuming interrupted call ...>  <unfinished ...>
> [pid  3237] restart_syscall(<... resuming interrupted call ...>
>
>
> * Sometimes ab pauses at the end but not all requests are successful; ab says:
>
> apr_socket_recv: Connection timed out (110)
> Total of 9932 requests completed
>
> The problem seems more acute if there's other application running on
> the system (e.g. right now I have kde, firefox, thunderbird active and
> I see more errors; note that nothing is using much CPU time). I've
> taken a sysrq-t log during one of ab pauses, it's attached.
>
>    
On my system,

#ab -n 100000 -c 1000 http://127.0.0.1/icons/poweredby.png

Also produces hangs/failures. But this happens regardless of the kernel 
version:
Stock 2.6.33, 2.6.33.5 from Fedora, 2.6.35-rc3, 2.6.35-rc3 with the 
semop changes reverted.

Thus I'd propose to close the current bug.
The IN_WAKEUP fix fixes the semop() and especially semtimedop() failures.

--
     Manfred