All, While studying the implementation of tasklets and softirq processing I came across certain issues which I have outlined below. The function mipsIRQ in the file mipsIRQ.s is the registered interrupt handler for all general purpose interrupts. The first thing that the function does is that it saves all registers. It then checks the CAUSE register to check the source of the interrupt. Currently all we are interested in is INT5 (Timer) and INT0 (i.e. all other devices) Consider a timer interrupt which would cause the code to jump to 0x8000:0180 and cause all the registers to be saved (SAVE_ALL). It would then jump to the mips_timer_interrupt function in the file time.c The function services the timer interrupt. At the end of the function there is an irq_exit and a check to see if there are any SOFT IRQ pending. If there are any the function jumps to the do_softirq function defined in the softirq.c. The function gets the softirq pending list, enables interrupts and cycles through all pending soft irq's calling the appropriate handlers. Remember that the interrupts are enabled while executing the various bottom half handlers. Now there are 2 cases that can happen 1. Since we have not exited the ISR and the exception level has still not been restored there can be no more interrupts that are generated in the system. In such a case does that mean that the all bottom half handlers pending execution will run with interrupts disabled. NOTE: This does not seem likely because the local_irq_enable routine calls _sti which clears the exception level in the status register and also sets the IE bit. 2. If we have large number of tasklets or if the bottom half handlers take time to execute, then we could get another timer interrupt or other device interrupts causing context saves which would cause the stack to grow and CRASH the system. Context is restored only when the code returns from do_softirq and uses the ret_from_irq. Is there anything that I am missing in this whole picture ? Thanks. - Pankaj
