https://issues.apache.org/bugzilla/show_bug.cgi?id=56034
Bug ID: 56034
Summary: CPU consumption due to circular linked list in
ap_core_input_filter()
Product: Apache httpd-2
Version: 2.2.15
Hardware: HP
OS: HP-UX
Status: NEW
Severity: normal
Priority: P2
Component: Core
Assignee: [email protected]
Reporter: [email protected]
We run Apache 2.2.15(+ fixes for certain CVEs) on HP Itanium server with HP-UX.
Once in a while, we observe ~100% CPU consumption by the httpd processes.
1. configuration
MPM worker configuration:
<IfModule mpm_worker_module>
ServerLimit 80
StartServers 67
MaxClients 4000
MinSpareThreads 3350
MaxSpareThreads 4000
ThreadsPerChild 50
MaxRequestsPerChild 1200
</IfModule>
web server: Reverse proxy
3rd party module: Oracle webgate
2. Logs
Please find the attached files:
a) stack trace : bt_all
b) top and syscall trace (top_syscall_trace)
c) Mapping between stack trace, source code and itanium assembly
code(trace_srccode_assemblyCode)
3. Trace identified from the core dump generated in that scenario:
syscall trace shows that main thread waits for the user space thread that run
ap_core_input_filter()
trace:
Thread 22 (system thread 1947121):
#0 0x40000000000977f0:2 in ap_core_input_filter () at core_filters.c:136
#1 0x40000000000c3f50:0 in ap_get_brigade () at util_filter.c:489
#2 0xc000000000ac76c0:0 in logio_in_filter () at mod_logio.c:129
#3 0x40000000000c3f50:0 in ap_get_brigade () at util_filter.c:489
#4 0x4000000000074980:0 in ap_rgetline_core () at protocol.c:231
#5 0xc000000004a33580:0 in ap_proxygetline () at mod_proxy_http.c:1658
#6 0xc000000004a338c0:0 in ap_proxy_http_process_response () at
mod_proxy_http.c:1733
#7 0xc000000004a35ee0:0 in proxy_http_handler () at mod_proxy_http.c:2434
#8 0xc000000004929a10:0 in proxy_run_scheme_handler () at mod_proxy.c:2675
#9 0xc000000004928b60:0 in proxy_handler () at mod_proxy.c:1024
#10 0x400000000009d2d0:0 in ap_run_handler ()
#11 0x400000000009e9e0:0 in ap_invoke_handler () at config.c:381
#12 0x40000000000cdec0:0 in ap_process_request () at http_request.c:282
#13 0x40000000000c5a40:0 in ap_process_http_connection () at http_core.c:190
#14 0x40000000000b8d20:0 in ap_process_connection () at connection.c:189
#15 0x40000000000de4c0:0 in process_socket () at worker.c:590
#16 0x40000000000df860:0 in worker_thread () at worker.c:974
#17 0xc000000006f95200:0 in dummy_worker () at threadproc/unix/thread.c:160
#18 0xc00000000013fb20:0 in __pthread_bound_body () at pthreads/pthread.c:4875
Eventhough it shows Line:136, actual loop happens @ line 141:
140 /* ### This is bad. */
141 BRIGADE_NORMALIZE(ctx->b);
Due to compiler optimzation and macro @ line 141, this line no is not shown in
trace.
As shown in the trace_srccode_assemblyCode attachment, linked list has become
circular because address and content of (ctx->b)->list))->next are same
(gdb) info register r44
gr44: 0x6000000000777de8
(gdb) x/gx0x6000000000777de8
0x6000000000777de8: 0x6000000000777de8
Prev’s value also contains the same.
(gdb) x/gx 0x6000000000774508
0x6000000000774508: 0x6000000000777de8
Please help to resolve this.
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