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[Bug kprobes/2568] New: KRetprobe on powerpc - Recursive post-handler - > fault-handler
- From: "bpeters at us dot ibm dot com" <sourceware-bugzilla at sourceware dot org>
- To: systemtap at sources dot redhat dot com
- Date: 13 Apr 2006 00:15:00 -0000
- Subject: [Bug kprobes/2568] New: KRetprobe on powerpc - Recursive post-handler - > fault-handler
- Reply-to: sourceware-bugzilla at sourceware dot org
Platform: PowerPC
Kernel: 2.6.16.5
If a kretprobe is registered without any assigned handlers for the embedded
kprobe, a recursive fault-handling loop is hit (See following printk output,
demonstrating the loop. The last number is the line number in the source file,
and the arrows indicate whether the printk is just before or just after the line
number mentioned:
[1986711.732589] <<< arch/powerpc/kernel/kprobes.c: 338 [Entered pre-handler code]
[1986711.732600] >>> arch/powerpc/kernel/kprobes.c: 339
[1986711.732610] <<< arch/powerpc/kernel/kprobes.c: 339
[1986711.732621] >>> arch/powerpc/kernel/kprobes.c: 346
[1986711.732633] <<< arch/powerpc/kernel/kprobes.c: 374 [fault handler code]
[1986711.732643] >>> arch/powerpc/kernel/kprobes.c: 375
[1986711.732654] <<< arch/powerpc/kernel/kprobes.c: 375
[1986711.732665] <<< arch/powerpc/kernel/kprobes.c: 374
[1986711.732675] >>> arch/powerpc/kernel/kprobes.c: 375
[1986711.732685] <<< arch/powerpc/kernel/kprobes.c: 375
[1986711.732697] <<< arch/powerpc/kernel/kprobes.c: 374
[1986711.732707] >>> arch/powerpc/kernel/kprobes.c: 375
......
....
....
After assigning NULL to each of the kprobe handlers, this recursive loop was
avoided.
retp_p->kp.pre_handler = (kprobe_pre_handler_t)NULL;
retp_p->kp.post_handler = (kprobe_post_handler_t)NULL;
retp_p->kp.fault_handler = (kprobe_fault_handler_t)NULL;
New trace:
[2005723.931159] <<< arch/powerpc/kernel/kprobes.c: 338 [Pre-handler]
[2005723.931169] >>> arch/powerpc/kernel/kprobes.c: 339
[2005723.931179] <<< arch/powerpc/kernel/kprobes.c: 339
[Fault handler never hit]
[2005723.931190] <<< arch/powerpc/kernel/kprobes.c: 327
[2005723.931201] >>> arch/powerpc/kernel/kprobes.c: 328
[2005723.931211] <<< arch/powerpc/kernel/kprobes.c: 328
[2005723.931221] <<< arch/powerpc/kernel/kprobes.c: 330
[2005723.931232] >>> arch/powerpc/kernel/kprobes.c: 331
[2005723.931243] <<< arch/powerpc/kernel/kprobes.c: 331
[2005723.931253] <<< arch/powerpc/kernel/kprobes.c: 349
[2005723.931264] >>> arch/powerpc/kernel/kprobes.c: 350
[2005723.931274] <<< arch/powerpc/kernel/kprobes.c: 350
[2005723.931284] <<< arch/powerpc/kernel/kprobes.c: 357
[2005723.931295] <<< arch/powerpc/kernel/kprobes.c: 359
[2005723.931305] >>> arch/powerpc/kernel/kprobes.c: 408
[2005723.931498] <<< arch/powerpc/kernel/kprobes.c: 145
[2005723.931509] >>> arch/powerpc/kernel/kprobes.c: 146
[2005723.931519] <<< arch/powerpc/kernel/kprobes.c: 146
[2005723.931530] >>> arch/powerpc/kernel/kprobes.c: 147
[2005723.931540] <<< arch/powerpc/kernel/kprobes.c: 147
[2005723.931550] >>> arch/powerpc/kernel/kprobes.c: 148
[2005723.931560] <<< arch/powerpc/kernel/kprobes.c: 148
[2005723.931570] <<< arch/powerpc/kernel/kprobes.c: 154
[2005723.931581] >>> arch/powerpc/kernel/kprobes.c: 155
[2005723.931591] <<< arch/powerpc/kernel/kprobes.c: 155
[2005723.931601] <<< kernel/kprobes.c: 176
[2005723.931609] >>> kernel/kprobes.c: 177
[2005723.931618] <<< kernel/kprobes.c: 177
[2005723.931627] >>> kernel/kprobes.c: 178
[2005723.931635] <<< kernel/kprobes.c: 178
[2005723.931645] <<< arch/powerpc/kernel/kprobes.c: 226
[2005723.931655] >>> arch/powerpc/kernel/kprobes.c: 227
[2005723.931666] <<< arch/powerpc/kernel/kprobes.c: 120
[2005723.931676] >>> arch/powerpc/kernel/kprobes.c: 121
[2005723.931687] <<< arch/powerpc/kernel/kprobes.c: 121
[2005723.931697] <<< arch/powerpc/kernel/kprobes.c: 227
[2005723.931707] <<< arch/powerpc/kernel/kprobes.c: 260
[2005723.931717] >>> arch/powerpc/kernel/kprobes.c: 261
[2005723.931728] <<< arch/powerpc/kernel/kprobes.c: 261
[2005723.931739] >>> arch/powerpc/kernel/kprobes.c: 262
[2005723.931749] <<< arch/powerpc/kernel/kprobes.c: 262
[2005723.931760] >>> arch/powerpc/kernel/kprobes.c: 263
[2005723.931770] <<< arch/powerpc/kernel/kprobes.c: 263
[2005723.931781] >>> arch/powerpc/kernel/kprobes.c: 264
[2005723.931791] <<< arch/powerpc/kernel/kprobes.c: 264
[2005723.931801] <<< arch/powerpc/kernel/kprobes.c: 266
[2005723.931812] >>> arch/powerpc/kernel/kprobes.c: 267
[2005723.931823] <<< arch/powerpc/kernel/kprobes.c: 267
[2005723.931833] <<< arch/powerpc/kernel/kprobes.c: 285
[2005723.931844] ***** Entered kretprobe handler
[2005723.931856] Ret handler hit :0 times. 0 times in time interval
[2005723.931867] Leaving KRetProbe Handler<0><<< arch/powerpc/kernel/kprobes.c: 290
Most likely cause is the post-handler is not being set to NULL by kprobes, when
called, it attempts to access a junk memory address, which then leads to the
fault-handler. This then attempts another invalid memory access, which loops
back to itself.
--
Summary: KRetprobe on powerpc - Recursive post-handler - > fault-
handler
Product: systemtap
Version: unspecified
Status: NEW
Severity: minor
Priority: P2
Component: kprobes
AssignedTo: systemtap at sources dot redhat dot com
ReportedBy: bpeters at us dot ibm dot com
http://sourceware.org/bugzilla/show_bug.cgi?id=2568
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