From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lee Schermerhorn Date: Wed, 09 Nov 2005 18:12:05 +0000 Subject: Question about interrupt enabling/disabling in kernel exit path Message-Id: <1131559925.5214.100.camel@localhost.localdomain> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org Hello: I have a question about enabling interrupts in the kernel exit path. Especially, in do_notify_resume_user(). I have work that I need to defer to this point, but it needs to run with interrupts enabled. I wanted to piggy back off TIF_NOTIFY_RESUME, because that is more or less generic code and gets handled in a C function where I can play the usual header games: static inline wrapper function when feature is configured; null macro when not. I see a comment at the beginning of ia64_leave_kernel that says that "work.need_resched, etc. mustn't get changed by this CPU before it returns to user- or fsys-mode, hence we disable interrupts early on." [This may be a stale comment. I.e., we now check for resched needed in current task's thread_info flags.] But, then I see later that when CONFIG_PREEMPT is set, we do enable interrupts and then re-disable them. Then I notice that after we return from do_notify_resume_user() we don't recheck TIF_NEED_RESCHED, etc. in the thread_info flags. So, maybe this is the issue? If I open an interrupt window in do_notify_resume_user(), 'NEED_RESCHED might get set and we wouldn't notice it on return to the assembly language code. [I might even sleep here. Is that a problem?] I took a look at the x86_64 and i386 versions and they always goes back to check for resched after calling their version of do_notify_resume() [no '_user suffix on the routine]. If this were the only issue with enabling interrupts in do_notify_resume_user(), I could change it to return non-zero if recheck is needed [zero in the usual case] and then go back and recheck thread_info flags. Regards, Lee