On Fri, Feb 29, 2008 at 10:18 PM, Vegard Nossum <vegard.nossum@xxxxxxxxx> wrote: > On Fri, Feb 29, 2008 at 1:34 AM, Peter Teoh <htmldeveloper@xxxxxxxxx> wrote: > > Sorry this part really puzzled me.... > > > > On Sat, Feb 9, 2008 at 8:10 AM, Rene Herman <rene.herman@xxxxxxxxxxxx> wrote: > > > > In the CPU's ALU. inode->i_size is a 64_bit integer, and access to it is > > > atomic on 64-bit. On a 32-bit arch though, a 64-bit load will be split in > > > two 32-bit ones where you can get an incoherent value if you're interrupted > > > between getting the low and the high 32-bit. > > > > > > Rene. > > > > > I understood what u are saying, as i_size is loff_t, and loff_t is > > defined as "long long". But the fact is this, of the thousands of > > assembly instructions in the kernel, in between any two, it can always > > be interrupted, so long as u ensure that the interrupt handler ensure > > that all the registers that it modified has been restored back to its > > original value upon returning. So I don't quite understand why it > > cannot be interrupted between the upper and lower half of the 32bit > > processing. > > Interrupts are used for many things. What if a timer interrupt occurs Yes, agreed, another tasks can switch in. > and it changes the current task? Then a different task can change the Yes, another task switch in, will have a totally different task context (correct term?) eg, stack register, local variables etc. But we are talking about local variable all the time, another task will never touch that local variable. For global - u need spin lock. So when it is return to the original task, the register value/local variable are all guaranteed to be as it is originally is. > variable before control is resumed in the original task. I hope this > explains your question. -- Regards, Peter Teoh -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
