[lkml]   [2010]   [Jun]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: PROBLEM: getpid() returning same value as getppid()
    On Wed 26-05-10 11:16:51, Nick Bowler wrote:
    > On 16:45 Wed 26 May , S?bastien Paumier wrote:
    > > Hi,
    > > here is a bug that occurs on my kernel 2.6.31-21, maybe with older ones.
    > > If a C program contains a function with the constructor attribute that
    > > calls getpid(), then, a call to syscall(SYS_fork) produces a son that
    > > obtains the same value calling getpid() or getppid().
    > The GNU C library caches the results of getpid, which is probably the
    > cause of your grief. This cache relies on the glibc wrappers for fork
    > and friends, which you have bypassed by using syscall directly.

    man page for getpid states that explicitly:
    Since glibc version 2.3.4, the glibc wrapper function for
    getpid() caches PIDs, so as to avoid additional system calls when
    a process calls getpid() repeatedly. Normally this caching is
    invisible, but its correct operation relies on support in the
    wrapper functions for fork(2), vfork(2), and clone(2):
    if an application bypasses the glibc wrappers for these system
    calls by using syscall(2), then a call to getpid() in the child
    will return the wrong value (to be precise: it will return the
    PID of the parent process). See also clone(2) for discussion
    of a case where getpid() may return the wrong value even when
    invoking clone(2) via the glibc wrapper function.

    > --
    > Nick Bowler, Elliptic Technologies (
    > --
    > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    > the body of a message to
    > More majordomo info at
    > Please read the FAQ at

    Michal Hocko
    L3 team
    SUSE LINUX s.r.o.
    Lihovarska 1060/12
    190 00 Praha 9
    Czech Republic

     \ /
      Last update: 2010-06-02 17:05    [W:0.029 / U:0.220 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site