From a0cd30ca3b8ad6880802c43402609de098918daa Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Tue, 7 Dec 2021 16:42:35 -0600 Subject: [PATCH] exit/s390: Remove dead reference to do_exit from copy_thread My s390 assembly is not particularly good so I have read the history of the reference to do_exit copy_thread and have been able to verify that do_exit is not used. The general argument is that s390 has been changed to use the generic kernel_thread and kernel_execve and the generic versions do not call do_exit. So it is strange to see a do_exit reference sitting there. The history of the do_exit reference in s390's version of copy_thread seems conclusive that the do_exit reference is something that lingers and should have been removed several years ago. Up through 8d19f15a60be ("[PATCH] s390 update (1/27): arch.") the s390 code made a call to the exit(2) system call when a kernel thread finished. Then kernel_thread_starter was added which branched directly to the value in register 11 when the kernel thread finshed. The value in register 11 was set in kernel_thread to "regs.gprs[11] = (unsigned long) do_exit" In commit 42cd14f38f3a ("s390: fold kernel_thread_helper() into ret_from_fork()") kernel_thread_starter was moved into entry.S and entry64.S unchanged (except for the syntax differences between inline assemly and in the assembly file). In commit 2801b948640e ("s390: switch to generic kernel_thread()") the assignment to "gprs[11]" was moved into copy_thread from the old kernel_thread. The helper kernel_thread_starter was still being used and was still branching to "%r11" at the end. In commit cb1d57402698 ("s390: switch to saner kernel_execve() semantics") kernel_thread_starter was changed to unconditionally branch to sysc_tracenogo instead to %r11 which held the value of do_exit. Unfortunately copy_thread was not updated to stop passing do_exit in "gprs[11]". In commit f6b35bb7a899 ("s390: convert to generic entry") kernel_thread_starter was replaced by __ret_from_fork. And the code still continued to pass do_exit in "gprs[11]" despite __ret_from_fork not caring in the slightest. Remove this dead reference to do_exit to make it clear that s390 is not doing anything with do_exit in copy_thread. Cc: Heiko Carstens Cc: Vasily Gorbik Cc: Christian Borntraeger Cc: Alexander Gordeev Cc: Martin Schwidefsky Cc: Al Viro Fixes: cb1d57402698 ("s390: switch to saner kernel_execve() semantics") History Tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git Acked-by: Heiko Carstens Signed-off-by: "Eric W. Biederman" --- arch/s390/kernel/process.c | 1 - 1 file changed, 1 deletion(-) diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c index e8858b2de24b7..71d86f73b02c9 100644 --- a/arch/s390/kernel/process.c +++ b/arch/s390/kernel/process.c @@ -139,7 +139,6 @@ int copy_thread(unsigned long clone_flags, unsigned long new_stackp, (unsigned long)__ret_from_fork; frame->childregs.gprs[9] = new_stackp; /* function */ frame->childregs.gprs[10] = arg; - frame->childregs.gprs[11] = (unsigned long)do_exit; frame->childregs.orig_gpr2 = -1; frame->childregs.last_break = 1; return 0; -- 2.39.5