signal: optimize 'sigaction' call path
Subsystems (2)
Quoted 8 lines
There is a set of syscalls in the kernel about 'sigaction'. All they end up with calling the helper '
do_sigaction', so the generic scheme is:- copy user data to kernel;
- 'do_sigaction';
- copy kernel data to user.
Quoted 5 lines
'
do_sigaction' checks 'signum' parameter before doing its main job. If this check fails syscall fails immediately, as well. But at this stage first copy is already done. And so there's a potential chance having it useless. It may affect performance significantly if user data was, say, swapped, and a fault was handled to obtain it.
Only if the signal number is wrong? So why do we care?
Quoted 2 lines
In this patch, 'signum' sanity check is moved out of '
do_sigaction' to a small function 'user_signal'. So we can call it before any copying.
...
Quoted 10 lines
arch/alpha/kernel/signal.c | 19 +++++++------- arch/mips/kernel/signal.c | 10 +++++--- arch/mips/kernel/signal32.c | 10 +++++--- arch/sparc/kernel/sys_sparc32.c | 10 ++++---- arch/sparc/kernel/sys_sparc_32.c | 10 ++++---- arch/sparc/kernel/sys_sparc_64.c | 10 ++++---- include/linux/sched.h | 2 +- include/linux/signal.h | 5 ++++ kernel/signal.c | 54 +++++++++++++++++++++------------------- 9 files changed, 71 insertions(+), 59 deletions(-)
And this blows the source and compiled code. Not too much, but this change should be justified somehow.
And to me this patch doesn't look like a cleanup, imho this sanity check makes more sense in one place.
Oleg.