[Bug nptl/27304] New: pthread_cond_destroy does not pass private flag to futex system calls

[Bug nptl/27304] New: pthread_cond_destroy does not pass private flag to futex system calls

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27304

            Bug ID: 27304
           Summary: pthread_cond_destroy does not pass private flag to
                    futex system calls
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: nptl
          Assignee: unassigned at sourceware dot org
          Reporter: fweimer at redhat dot com
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

Commit dc6cfdc934db9997c33728082d63552b9eee4563 ("nptl: Move
pthread_cond_destroy implementation into libc") dropped use of the
process-shared flag because of this optimization in
sysdeps/nptl/lowlevellock-futex.h:

# if IS_IN (libc) || IS_IN (rtld)
/* In libc.so or ld.so all futexes are private.  */
#  define __lll_private_flag(fl, private)                       \
  ({                                                            \
    /* Prevent warnings in callers of this macro.  */           \
    int __lll_private_flag_priv __attribute__ ((unused));       \
    __lll_private_flag_priv = (private);                        \
    ((fl) | FUTEX_PRIVATE_FLAG);                                \
  })
# else
#  define __lll_private_flag(fl, private) \
  (((fl) | FUTEX_PRIVATE_FLAG) ^ (private))
# endif

I think the fix is to remove the optimization because it is unused. The
internal locks are always private, so the optimization does not matter to them.

On x86-64, pthread_cond_destroy is the only place where the alternative macro
definition results in changed machine code, but we do not actually want this
change there (because it probably breaks process-shared condition variables).

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug nptl/27304] pthread_cond_destroy does not pass private flag to futex system calls

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27304

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at sourceware dot org   |fweimer at redhat dot com
                 CC|                            |fweimer at redhat dot com
             Status|NEW                         |ASSIGNED

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug nptl/27304] pthread_cond_destroy does not pass private flag to futex system calls

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27304

--- Comment #1 from Florian Weimer <fweimer at redhat dot com> ---
Patch posted:
https://sourceware.org/pipermail/libc-alpha/2021-February/122181.html

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug nptl/27304] pthread_cond_destroy does not pass private flag to futex system calls

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27304

--- Comment #2 from Florian Weimer <fweimer at redhat dot com> ---
Note that this is sadly unrelated to the libdb/RPM database corruption we see
on s390x; we have not backported this into the glibc 2.28 branch where we see
this.

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug nptl/27304] pthread_cond_destroy does not pass private flag to futex system calls

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=27304

--- Comment #3 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Florian Weimer <fw@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c4ad832276f4dadfa40904109b26a521468f66bc

commit c4ad832276f4dadfa40904109b26a521468f66bc
Author: Florian Weimer <fweimer@redhat.com>
Date:   Thu Feb 4 15:00:20 2021 +0100

    nptl: Remove private futex optimization [BZ #27304]

    It is effectively used, unexcept for pthread_cond_destroy, where we do
    not want it; see bug 27304.  The internal locks do not support a
    process-shared mode.

    This fixes commit dc6cfdc934db9997c33728082d63552b9eee4563 ("nptl:
    Move pthread_cond_destroy implementation into libc").

    Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug nptl/27304] pthread_cond_destroy does not pass private flag to futex system calls

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27304

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #4 from Florian Weimer <fweimer at redhat dot com> ---
Fixed for glibc 2.34.

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug nptl/27304] pthread_cond_destroy does not pass private flag to futex system calls

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27304

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |2.34

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug nptl/27304] pthread_cond_destroy does not pass private flag to futex system calls

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27304

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://github.com/linux-te
                   |                            |st-project/ltp/issues/746

--- Comment #5 from Florian Weimer <fweimer at redhat dot com> ---
It turns out that LTP actually tests for this bug.

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug nptl/27304] pthread_cond_destroy does not pass private flag to futex system calls

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=27304

--- Comment #6 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The release/2.33/master branch has been updated by Florian Weimer
<fw@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=79c6be6a0ad59e28cfb73ad6cae6b073e22836e3

commit 79c6be6a0ad59e28cfb73ad6cae6b073e22836e3
Author: Florian Weimer <fweimer@redhat.com>
Date:   Thu Feb 4 15:00:20 2021 +0100

    nptl: Remove private futex optimization [BZ #27304]

    It is effectively used, unexcept for pthread_cond_destroy, where we do
    not want it; see bug 27304.  The internal locks do not support a
    process-shared mode.

    This fixes commit dc6cfdc934db9997c33728082d63552b9eee4563 ("nptl:
    Move pthread_cond_destroy implementation into libc").

    Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
    (cherry picked from commit c4ad832276f4dadfa40904109b26a521468f66bc)

-- 
You are receiving this mail because:
You are on the CC list for the bug.