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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