Remove cached PID/TID in clone

System Internals / glibc - Adhemerval Zanella [linaro.org] - 24 November 2016 15:38 UTC

This patch remove the PID cache and usage in current GLIBC code. Current usage is mainly used a performance optimization to avoid the syscall, however it adds some issues:

- The exposed clone syscall will try to set pid/tid to make the new thread somewhat compatible with current GLIBC assumptions. This cause a set of issue with new workloads and usecases (such as BZ#17214 and [1]) as well for new internal usage of clone to optimize other algorithms (such as clone plus CLONE_VM for posix_spawn, BZ#19957).

- The caching complexity also added some bugs in the past [2] [3] and requires more effort of each port to handle such requirements (for both clone and vfork implementation).

- Caching performance gain in mainly on getpid and some specific code paths. The getpid performance leverage is questionable [4], either by the idea of getpid being a hotspot as for the getpid implementation itself (if it is indeed a justifiable hotspot a
vDSO symbol could let to a much more simpler solution).

Other usage is mainly for non usual code paths, such as pthread cancellation signal and handling.

For thread creation (on stack allocation) the code simplification in fact adds some performance gain due the no need of transverse the stack cache and invalidate each element pid.

Other thread usages will require a direct getpid syscall, such as cancellation/setxid signal, thread cancellation, thread fail path (at create_thread), and thread signal (pthread_kill and pthread_sigqueue). However these are hardly usual hotspots and I think adding a syscall is justifiable.

It also simplifies both the clone and vfork arch-specific implementation. And by review each fork implementation there are some discrepancies that this patch also solves:

- microblaze clone/vfork does not set/reset the pid/tid field
- hppa uses the default vfork implementation that fallback to fork. Since vfork is deprecated I do not think we should bother with it.

The patch also removes the TID caching in clone. My understanding for such semantic is try provide some pthread usage after a user program issue clone directly (as done by thread creation with CLONE_PARENT_SETTID and pthread tid member). However, as stated before in multiple discussions threads, GLIBC provides clone syscalls without further supporting all this semantics.

I ran a full make check on x86_64, x32, i686, armhf, aarch64, and powerpc64le. For sparc32, sparc64, and mips I ran the basic fork and vfork tests from posix/ folder (on a qemu system). So it would require further testing on alpha, hppa, ia64, m68k, nios2, s390, sh, and tile (I excluded microblaze because it is already implementing the patch semantic regarding clone/vfork).

[1] https://codereview.chromium.org/800183004/ [2] https://sourceware.org/ml/libc-alpha/2006-07/msg00123.html [3] https://sourceware.org/bugzilla/show_bug.cgi?id=15368 [4] http://yarchive.net/comp/linux/getpid_caching.html

- sysdeps/nptl/fork.c (__libc_fork): Remove pid cache setting.
- nptl/allocatestack.c (allocate_stack): Likewise. (__reclaim_stacks): Likewise. (setxid_signal_thread): Obtain pid through syscall.
- nptl/nptl-init.c (sigcancel_handler): Likewise. (sighandle_setxid): Likewise.
- nptl/pthread_cancel.c (pthread_cancel): Likewise.
- sysdeps/unix/sysv/linux/pthread_kill.c (__pthread_kill): Likewise.
- sysdeps/unix/sysv/linux/pthread_sigqueue.c (pthread_sigqueue): Likewise.
- sysdeps/unix/sysv/linux/createthread.c (create_thread): Likewise.
- sysdeps/unix/sysv/linux/getpid.c: Remove file.
- nptl/descr.h (struct pthread): Change comment about pid value.
- nptl/pthread_getattr_np.c (pthread_getattr_np): Remove thread pid assert.
- sysdeps/unix/sysv/linux/pthread-pids.h (__pthread_initialize_pids): Do not set pid value.
- nptl_db/td_ta_thr_iter.c (iterate_thread_list): Remove thread pid cache check.
- nptl_db/td_thr_validate.c (td_thr_validate): Likewise.
- sysdeps/aarch64/nptl/tcb-offsets.sym: Remove pid offset.
- sysdeps/alpha/nptl/tcb-offsets.sym: Likewise.
- sysdeps/arm/nptl/tcb-offsets.sym: Likewise.
- sysdeps/hppa/nptl/tcb-offsets.sym: Likewise.
- sysdeps/i386/nptl/tcb-offsets.sym: Likewise.
- sysdeps/ia64/nptl/tcb-offsets.sym: Likewise.
- sysdeps/m68k/nptl/tcb-offsets.sym: Likewise.
- sysdeps/microblaze/nptl/tcb-offsets.sym: Likewise.
- sysdeps/mips/nptl/tcb-offsets.sym: Likewise.
- sysdeps/nios2/nptl/tcb-offsets.sym: Likewise.
- sysdeps/powerpc/nptl/tcb-offsets.sym: Likewise.
- sysdeps/s390/nptl/tcb-offsets.sym: Likewise.
- sysdeps/sh/nptl/tcb-offsets.sym: Likewise.
- sysdeps/sparc/nptl/tcb-offsets.sym: Likewise.
- sysdeps/tile/nptl/tcb-offsets.sym: Likewise.
- sysdeps/x86_64/nptl/tcb-offsets.sym: Likewise.
- sysdeps/unix/sysv/linux/aarch64/clone.S: Remove pid and tid caching.
- sysdeps/unix/sysv/linux/alpha/clone.S: Likewise.
- sysdeps/unix/sysv/linux/arm/clone.S: Likewise.
- sysdeps/unix/sysv/linux/hppa/clone.S: Likewise.
- sysdeps/unix/sysv/linux/i386/clone.S: Likewise.
- sysdeps/unix/sysv/linux/ia64/clone2.S: Likewise.
- sysdeps/unix/sysv/linux/mips/clone.S: Likewise.
- sysdeps/unix/sysv/linux/nios2/clone.S: Likewise.
- sysdeps/unix/sysv/linux/powerpc/powerpc32/clone.S: Likewise.
- sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S: Likewise.
- sysdeps/unix/sysv/linux/s390/s390-32/clone.S: Likewise.
- sysdeps/unix/sysv/linux/s390/s390-64/clone.S: Likewise.
- sysdeps/unix/sysv/linux/sh/clone.S: Likewise.
- sysdeps/unix/sysv/linux/sparc/sparc32/clone.S: Likewise.
- sysdeps/unix/sysv/linux/sparc/sparc64/clone.S: Likewise.
- sysdeps/unix/sysv/linux/tile/clone.S: Likewise.
- sysdeps/unix/sysv/linux/x86_64/clone.S: Likewise.
- sysdeps/unix/sysv/linux/aarch64/vfork.S: Remove pid set and reset.
- sysdeps/unix/sysv/linux/alpha/vfork.S: Likewise.
- sysdeps/unix/sysv/linux/arm/vfork.S: Likewise.
- sysdeps/unix/sysv/linux/i386/vfork.S: Likewise.
- sysdeps/unix/sysv/linux/ia64/vfork.S: Likewise.
- sysdeps/unix/sysv/linux/m68k/clone.S: Likewise.
- sysdeps/unix/sysv/linux/m68k/vfork.S: Likewise.
- sysdeps/unix/sysv/linux/mips/vfork.S: Likewise.
- sysdeps/unix/sysv/linux/nios2/vfork.S: Likewise.
- sysdeps/unix/sysv/linux/powerpc/powerpc32/vfork.S: Likewise.
- sysdeps/unix/sysv/linux/powerpc/powerpc64/vfork.S: Likewise.
- sysdeps/unix/sysv/linux/s390/s390-32/vfork.S: Likewise.
- sysdeps/unix/sysv/linux/s390/s390-64/vfork.S: Likewise.
- sysdeps/unix/sysv/linux/sh/vfork.S: Likewise.
- sysdeps/unix/sysv/linux/sparc/sparc32/vfork.S: Likewise.
- sysdeps/unix/sysv/linux/sparc/sparc64/vfork.S: Likewise.
- sysdeps/unix/sysv/linux/tile/vfork.S: Likewise.
- sysdeps/unix/sysv/linux/x86_64/vfork.S: Likewise.
- sysdeps/unix/sysv/linux/tst-clone2.c (f): Remove direct pthread struct access. (clone_test): Remove function. (do_test): Rewrite to take in consideration pid is not cached anymore.

c579f48 Remove cached PID/TID in clone
ChangeLog | 81 +++++++++++++++
nptl/allocatestack.c | 20 +---
nptl/descr.h | 4 +-
nptl/nptl-init.c | 15 +--
nptl/pthread_cancel.c | 18 +---
nptl/pthread_getattr_np.c | 1 -
nptl_db/structs.def | 1 -
nptl_db/td_ta_thr_iter.c | 56 ++++-------
nptl_db/td_thr_validate.c | 23 -----
sysdeps/aarch64/nptl/tcb-offsets.sym | 1 -
sysdeps/alpha/nptl/tcb-offsets.sym | 1 -
sysdeps/arm/nptl/tcb-offsets.sym | 1 -
sysdeps/hppa/nptl/tcb-offsets.sym | 2 -
sysdeps/i386/nptl/tcb-offsets.sym | 1 -
sysdeps/ia64/nptl/tcb-offsets.sym | 1 -
sysdeps/m68k/nptl/tcb-offsets.sym | 1 -
sysdeps/microblaze/nptl/tcb-offsets.sym | 1 -
sysdeps/mips/nptl/tcb-offsets.sym | 1 -
sysdeps/nios2/nptl/tcb-offsets.sym | 1 -
sysdeps/nptl/fork.c | 12 ---
sysdeps/powerpc/nptl/tcb-offsets.sym | 1 -
sysdeps/s390/nptl/tcb-offsets.sym | 1 -
sysdeps/sh/nptl/tcb-offsets.sym | 1 -
sysdeps/sparc/nptl/tcb-offsets.sym | 1 -
sysdeps/tile/nptl/tcb-offsets.sym | 1 -
sysdeps/unix/sysv/linux/aarch64/clone.S | 10 --
sysdeps/unix/sysv/linux/aarch64/vfork.S | 17 ----
sysdeps/unix/sysv/linux/alpha/clone.S | 16 ---
sysdeps/unix/sysv/linux/alpha/vfork.S | 15 ---
sysdeps/unix/sysv/linux/arm/clone.S | 10 --
sysdeps/unix/sysv/linux/arm/vfork.S | 15 ---
sysdeps/unix/sysv/linux/createthread.c | 6 +-
sysdeps/unix/sysv/linux/getpid.c | 64 ------------
sysdeps/unix/sysv/linux/hppa/clone.S | 12 ---
sysdeps/unix/sysv/linux/hppa/pt-vfork.S | 26 -----
sysdeps/unix/sysv/linux/i386/clone.S | 15 ---
sysdeps/unix/sysv/linux/i386/vfork.S | 19 ----
sysdeps/unix/sysv/linux/ia64/clone2.S | 14 +--
sysdeps/unix/sysv/linux/ia64/vfork.S | 20 ----
sysdeps/unix/sysv/linux/m68k/clone.S | 13 ---
sysdeps/unix/sysv/linux/m68k/vfork.S | 20 ----
sysdeps/unix/sysv/linux/mips/clone.S | 13 ---
sysdeps/unix/sysv/linux/mips/vfork.S | 19 ----
sysdeps/unix/sysv/linux/nios2/clone.S | 8 --
sysdeps/unix/sysv/linux/nios2/vfork.S | 10 --
sysdeps/unix/sysv/linux/powerpc/powerpc32/clone.S | 9 --
sysdeps/unix/sysv/linux/powerpc/powerpc32/vfork.S | 26 -----
sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S | 9 --
sysdeps/unix/sysv/linux/powerpc/powerpc64/vfork.S | 23 -----
sysdeps/unix/sysv/linux/pthread-pids.h | 2 +-
sysdeps/unix/sysv/linux/pthread_kill.c | 11 +-
sysdeps/unix/sysv/linux/pthread_sigqueue.c | 15 +--
sysdeps/unix/sysv/linux/raise.c | 7 --
sysdeps/unix/sysv/linux/s390/s390-32/clone.S | 7 --
sysdeps/unix/sysv/linux/s390/s390-32/vfork.S | 12 ---
sysdeps/unix/sysv/linux/s390/s390-64/clone.S | 9 --
sysdeps/unix/sysv/linux/s390/s390-64/vfork.S | 13 ---
sysdeps/unix/sysv/linux/sh/clone.S | 22 +---
sysdeps/unix/sysv/linux/sh/vfork.S | 21 ----
sysdeps/unix/sysv/linux/sparc/sparc32/clone.S | 7 --
sysdeps/unix/sysv/linux/sparc/sparc32/vfork.S | 10 --
sysdeps/unix/sysv/linux/sparc/sparc64/clone.S | 7 --
sysdeps/unix/sysv/linux/sparc/sparc64/vfork.S | 10 --
sysdeps/unix/sysv/linux/syscalls.list | 1 +
sysdeps/unix/sysv/linux/tile/clone.S | 16 ---
sysdeps/unix/sysv/linux/tile/vfork.S | 28 ------
sysdeps/unix/sysv/linux/tst-clone2.c | 111 ++++++++-------------
sysdeps/unix/sysv/linux/x86_64/clone.S | 8 --
sysdeps/unix/sysv/linux/x86_64/vfork.S | 18 ----
sysdeps/x86_64/nptl/tcb-offsets.sym | 1 -
70 files changed, 165 insertions(+), 827 deletions(-)

Upstream: sourceware.org

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