On Sun, Mar 11, 2012 at 8:33 PM, Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> wrote: > On Sun, Mar 11, 2012 at 08:18:32PM +0530, santosh prasad nayak wrote: >> On Sun, Mar 11, 2012 at 8:06 PM, Russell King - ARM Linux >> <linux@xxxxxxxxxxxxxxxx> wrote: >> > On Sun, Mar 11, 2012 at 07:47:27PM +0530, santosh prasad nayak wrote: >> >> Not to use in_atomic() in driver code. >> >> >> >> Following article inspired me to do the change. >> >> http://lwn.net/Articles/274695/ >> >> >> >> "in_atomic() is for core kernel use only. Because in special >> >> circumstances (ie: kmap_atomic()) we run inc_preempt_count() even on >> >> non-preemptible kernels to tell the per-arch fault handler that it was >> >> invoked by copy_*_user() inside kmap_atomic(), and it must fail. >> >> In other words, in_atomic() works in a specific low-level situation, >> >> but it was never meant to be used in a wider context. Its placement in >> >> hardirq.h next to macros which can be used elsewhere was, thus, almost >> >> certainly a mistake. As Alan Stern pointed out, the fact that Linux >> >> Device Drivers recommends the use of in_atomic() will not have helped >> >> the situation. Your editor recommends that the authors of that book be >> >> immediately sacked. " >> >> >> >> In the present case, we just check whether its an IRQ context or user >> >> context. So for that >> >> we can use "in_interrupt()". >> >> >> >> Greg also mentions the same in the following mail. >> >> http://www.spinics.net/lists/newbies/msg43402.html >> > >> > In which case, we'll just have to do mdelay() and forget about allowing >> > anything else to run for the 20ms that we need to sleep. Sucky but >> > that's the way things are. >> >> mdelay() or msleep() are there before. I did not change that. >> >> >> my point is : in_atomic() vs "in_interrupt()". >> We should avoid to use "in_atomic()" in driver code. >> >> In the present case to check IRQ context "in_interrupt()" should be preferred. > > in_interrupt() won't tell us if we're being called with spinlocks held, > which _is_ a possibility because this can be called from printk(), for > oops dumps and the like. > > in_interrupt() just means that we're inside a hard or soft interrupt, > or nmi. It says nothing about whether msleep() is possible. in_atomic() is also not error free. I found following comment in include/linux/hardirq.h. How do you handle it in non-preemptible kernel ? /* * Are we running in atomic context? WARNING: this macro cannot * always detect atomic context; in particular, it cannot know about * held spinlocks in non-preemptible kernels. Thus it should not be * used in the general case to determine whether sleeping is possible. * Do not use in_atomic() in driver code. */ #define in_atomic() ((preempt_count() & ~PREEMPT_ACTIVE) != 0) regards Santosh -- To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
