2.4.29 arch/i386/entry.S question

[Der Herr Hofrat <der.herr@hofr.at>]

Hi  !

Kernel 2.4.29 (unpatched)
Arch   i386

 I'm trying to understand the details of what is going on here. As I 
understand this, the cli/sti braces are intended for atomicity of 
need_resched and signals, but what does the comment at the sti them mean ?
can one get to signal_return without entering at ret_from_sys_call ?
I assumed the sti is just balancing the cli - woong ?

arch/i386/kernel/entry.S:

ENTRY(ret_from_sys_call)
	cli				# need_resched and signals atomic test
	cmpl $0,need_resched(%ebx)
	jne reschedule
	cmpl $0,sigpending(%ebx)
	jne signal_return
restore_all:
	RESTORE_ALL

	ALIGN
signal_return:
	sti				# we can get here from an interrupt handler

 Also if need_resched and sigpending were not handled atomically, that is if
one removes the cli/sti - would that actually break anything ? It seems that
it could be inefficient as one would reschedule in cases without this
being necessary, and could call do_signal without that it is needed, or is
there more to it ? I removed the cli/sti and rebuilt the system, but could
not find any imediate problems (which off course does not really say much
yet).

thx !
hofrat
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