Hi Arun, When I used word nested interrupt, I meant that in my interrupt handler I am enabling interrupts. and about "what made you believe we need system mode to support nesting?" I asked this question on SO, here is the link for its answer http://stackoverflow.com/a/22500017/769260 And thanks for your prompt answer :) Regards Rahul On Tue, Mar 25, 2014 at 4:45 PM, Arun KS <getarunks@xxxxxxxxx> wrote: > On Tue, Mar 25, 2014 at 4:40 PM, Arun KS <getarunks@xxxxxxxxx> wrote: >> Hello Rahul, >> >> On Tue, Mar 25, 2014 at 4:10 PM, Rahul Garg <rahul.lnmiit@xxxxxxxxx> wrote: >>> Hi Arun, >>> >>> Lines from Robert Love : >>> >>> Early in the 2.6 kernel process, an option was added to reduce the >>> stack size from two >>> pages down to one, providing only a 4KB stack on 32-bit systems.This >>> reduced memory >>> pressure because every process on the system previously needed two >>> pages of contiguous, >>> nonswappable kernel memory.To cope with the reduced stack size, >>> interrupt handlers >>> were given their own stack, one stack per processor, one page in >>> size.This stack is referred >>> to as the interrupt stack.Although the total size of the interrupt >>> stack is half that of the >>> original shared stack, the average stack space available is greater >>> because interrupt handlers >>> get the full page of memory to themselves. >> >> Kernel stack size is architecture dependent. Some architecture uses >> CONFIG_4KSTACKS to choose 4K stacks. >> >> Where as in arm, it is always 8KB. >> >> File:arch/arm/include/asm/thread_info.h >> #define THREAD_SIZE_ORDER 1 >> #define THREAD_SIZE 8192 >> #define THREAD_START_SP (THREAD_SIZE - 8) >> >>> >>> >>> So with these lines, it is clear that interrupt stack is used by >>> interrupt handlers. So can you please re-confirm your answer ? >> On ARM when there is an irq, the processor switches to irq mode. But >> the kernel switches to svc mode immediately and uses SVC stack, ie the >> stack of the current process. >> >> Why do you believe my be? :-) >> If you want re-confirmation, go through arch/arm/kernel/entry-armv.S >> >> Thanks, >> Arun >>> >>> And one more thing, as you mentioned only interrupt, undefined and >>> abort have stack, So how nested interrupt is handled because for that >>> we need System mode stack ? > Interrupts are no more nested in linux kernel, > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/kernel/irq/handle.c?id=e58aa3d2d0cc01ad8d6f7f640a0670433f794922 > > But nested exceptions(data, prefetch aborts etc) can still happen. > > And, what made you believe we need system mode to support nesting? > What difference does it make if it is svc mode? > > Thanks, > Arun > > >> ARM linux never use system mode for anything. >> >>> >>> Regards >>> Rahul >>> >>> On Tue, Mar 25, 2014 at 3:06 PM, Arun KS <getarunks@xxxxxxxxx> wrote: >>>> On Tue, Mar 25, 2014 at 2:58 PM, Arun KS <getarunks@xxxxxxxxx> wrote: >>>>> Hello Rahul, >>>>> >>>>> On Tue, Mar 25, 2014 at 6:29 AM, Rahul Garg <rahul.lnmiit@xxxxxxxxx> wrote: >>>>>> As I understand every process have a user stack and kernel stack. >>>>> True. >>>>> >>>>>> Apart from that there is a stack for every mode in ARM achitecture. So >>>>> This is wrong. >>>>> Only irq, abort and undefined modes have stacks in linux. That too is >>>>> very limited, 3 bytes per mode per cpu. >>>>> Have a look at arch/arm/kernel/irq.c >>>> Sorry. Wrong file, its at arch/arm/kernel/setup.c >>>> >>>> Thanks, >>>> Arun >>>>> struct stack { >>>>> u32 irq[3]; >>>>> u32 abt[3]; >>>>> u32 und[3]; >>>>> } ____cacheline_aligned; >>>>> >>>>> kernel runs in SVC mode and the stack used belong to the kernel stack >>>>> of the current task. >>>>> Even irq, abort and undefined exception handlers use kernel stack of >>>>> current task. All the exception >>>>> handlers switch to SVC mode at a very early stage and use kernel >>>>> stack. Those 3 bytes are used >>>>> as stack just during the transition phase(for example transition from >>>>> irq to svc mode during and interrupt). >>>>> >>>>> Thanks, >>>>> Arun >>>>>> I want to know How different stack and stack pointer works in ARM >>>>>> modes? Also when this kernel stack associated with the process will be >>>>>> used ? >>>>>> >>>>>> _______________________________________________ >>>>>> Kernelnewbies mailing list >>>>>> Kernelnewbies@xxxxxxxxxxxxxxxxx >>>>>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
