[Bug nptl/5983] New: Stale threads from TD_TA_THR_ITER of the FORK child during PTRACE_SYSCALL

[jan dot kratochvil at redhat dot com]

The child of FORK becomes (later) singlethreaded, unfortunately it gets caught
too early by PTRACE_O_TRACEFORK and the child appears as multithreaded to
nptl_db that time.


gcc -ggdb3 -Wall -Werror -o forktest forktest.c -lthread_db -ldw -lelf -lebl
-ldl -pthread
outputs:
        child = 9097
        LWP = 9097 TID = 0x2aaaaace9290
        LWP = 9098 TID = 0x40a00950
        child2 = 9099
        LWP = 9099 TID = 0x2aaaaace9290
        LWP = 9098 TID = 0x40a00950             <- stale thread
while it should be:
        child = 9097
        LWP = 9097 TID = 0x2aaaaace9290
        LWP = 9098 TID = 0x40a00950
        child2 = 9099
        LWP = 9099 TID = 0x2aaaaace9290


Untested glibc fix attached but just the part modifying `nptl_db/structs.def'
completely breaks nptl_db for me.

This patch variant has some performance hit calling __getpid(), the other way
would require adding some new field to `struct pthread'.


Going to fix it myself but still did not find enough time so at least making the
problem public.

-- 
           Summary: Stale threads from TD_TA_THR_ITER of the FORK child
                    during PTRACE_SYSCALL
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: minor
          Priority: P2
         Component: nptl
        AssignedTo: drepper at redhat dot com
        ReportedBy: jan dot kratochvil at redhat dot com
                CC: glibc-bugs at sources dot redhat dot com
  GCC host triplet: x86_64-unknown-linux-gnu


http://sourceware.org/bugzilla/show_bug.cgi?id=5983

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