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Full support for /proc/sys/kernel/pid_max changing during a process changing at runtime #2

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richardstartin opened this issue Jul 19, 2023 · 0 comments
Open

Full support for /proc/sys/kernel/pid_max changing during a process changing at runtime #2

richardstartin opened this issue Jul 19, 2023 · 0 comments

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@richardstartin
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Currently the profiler assumes that the value stored at /proc/sys/kernel/pid_max does not increase at runtime. The value is used for sizing various internal data structures, for example:

  • the number of perf event subscriptions (how many threads can be profiled)
  • the size of wallclock thread filter
  • the size of the trace context lookup

In some scenarios users may increase this value during a process's lifetime which violates this assumption. Currently there is a workaround to floor the value read from /proc/sys/kernel/pid_max at 131072, but profile sample labelling would be broken (but not crash) if this number of threads is ever exceeded.
r1viollet added a commit that referenced this issue Oct 23, 2024
@r1viollet
Undefined behaviour fix
d349f45 
Avoid shifting a negative value
This was raised by asan nightly runs

> Task :ddprof-test:testClasses
ddprof-lib/src/main/cpp/vmStructs.cpp:816:34: runtime error: left shift of negative value -1
    #0 0x7f6f6bd20631 in ScopeDesc::readInt()
    #1 0x7f6f6bce54a6 in ScopeDesc::decode(int)
    #2 0x7f6f6bce7fb0 in StackWalker::walkVM(void*, ASGCT_CallFrame*, int, void const*, void const*)
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