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SubjectRe: 2.6.35-rc3 deadlocks on semaphore operations
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


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