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Issue with stack) on 6.x kernels

DISCUSSION Kris Van Hees 2 participants 3 messages May 1, 2024

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Kris Van Hees

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#0 lore raw

Newer 6.x kernels (I tried 6.5.0 and 6.8.0) seem to behave differently for stack() than e.g. 5,15,0, Test test/unittest/aggs/tst.stack.d FAILs on those 6.x kernels whereas it passes on 5.15.0. I am not sure yet why there is a difference, but Eugene, perhaps you can take a look into this?

Kris

author
#1 lore raw
Quoted 6 lines · Kris Van Hees

Newer 6.x kernels (I tried 6.5.0 and 6.8.0) seem to behave differently for stack() than e.g. 5,15,0, Test test/unittest/aggs/tst.stack.d FAILs on those 6.x kernels whereas it passes on 5.15.0. I am not sure yet why there is a difference, but Eugene, perhaps you can take a look into this?

Kris

Here is an example:

$ sudo ./build/run-dtrace -s test/unittest/aggs/tst.stack.d 
[sudo] password for kvanhees: 
  0xffffffffc0129e86                                
  0xffffffffc0129e86                                
  0xffffffffc0129e86                                
              0xffffffffc0130250
              0xffffffffc0130250
              0xffffffffc012b2bb
              0xffffffffc012b83c
              vmlinux`schedule+0x9

The strange thing is that it actually does give good results at times.

So I am not sure what is going on.

#2 lore raw
Quoted 22 lines · Kris Van Hees via DTrace-devel
Quoted 6 lines · Kris Van Hees

Newer 6.x kernels (I tried 6.5.0 and 6.8.0) seem to behave differently for stack() than e.g. 5,15,0, Test test/unittest/aggs/tst.stack.d FAILs on those 6.x kernels whereas it passes on 5.15.0. I am not sure yet why there is a difference, but Eugene, perhaps you can take a look into this?

Kris

Here is an example:

$ sudo ./build/run-dtrace -s test/unittest/aggs/tst.stack.d 
[sudo] password for kvanhees: 
  0xffffffffc0129e86                                
  0xffffffffc0129e86                                
  0xffffffffc0129e86                                
              0xffffffffc0130250
              0xffffffffc0130250
              0xffffffffc012b2bb
              0xffffffffc012b83c
              vmlinux`schedule+0x9
Quoted 4 lines

The strange thing is that it actually does give good results at times.

So I am not sure what is going on.

here's an upstream thread discussing stacks + fentry:

https://lore.kernel.org/bpf/49b9b6f.1279.18aadb90e05.Coremail.chang-liu22@mails.tsinghua.edu.cn/

Looks like the top few entries relate to the trampoline and fentry program..

Quoted 4 lines

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