Hi all-
I'm working on my kentry patchset, and I encountered:
commit 56e62a73702836017564eaacd5212e4d0fa1c01d
Author: Sven Schnelle <svens@xxxxxxxxxxxxx>
Date: Sat Nov 21 11:14:56 2020 +0100
s390: convert to generic entry
As part of this work, I was cleaning up the generic syscall helpers,
and I encountered the goodies in do_syscall() and __do_syscall().
I'm trying to wrap my head around the current code, and I'm rather confused.
1. syscall_exit_to_user_mode_work() does *all* the exit work, not just
the syscall exit work. So a do_syscall() that gets called twice will
do the loopy part of the exit work (e.g. signal handling) twice. Is
this intentional? If so, why?
2. I don't understand how this PIF_SYSCALL_RESTART thing is supposed
to work. Looking at the code in Linus' tree, if a signal is pending
and a syscall returns -ERESTARTSYS, the syscall will return back to
do_syscall(). The work (as in (1)) gets run, calling do_signal(),
which will notice -ERESTARTSYS and set PIF_SYSCALL_RESTART.
Presumably it will also push the signal frame onto the stack and aim
the return address at the svc instruction mentioned in the commit
message from "s390: convert to generic entry". Then __do_syscall()
will turn interrupts back on and loop right back into do_syscall().
That seems incorrect.
Can you enlighten me? My WIP tree is here:
https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/log/?h=x86/kentry
Here are my changes to s390, and I don't think they're really correct:
https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/diff/arch/s390/kernel/syscall.c?h=x86/kentry&id=58a459922be0fb8e0f17aeaebcb0ac8d0575a62c
