On Fri, 2019-06-28 at 06:33:18 UTC, Nicholas Piggin wrote: > The bad stack test in interrupt handlers has a few problems. For > performance it is taken in the common case, which is a fetch bubble > and a waste of i-cache. > > For code development and maintainence, it requires yet another stack > frame setup routine, and that constrains all exception handlers to > follow the same register save pattern which inhibits future > optimisation. > > Remove the test/branch and replace it with a trap. Teach the program > check handler to use the emergency stack for this case. > > This does not result in quite so nice a message, however the SRR0 and > SRR1 of the crashed interrupt can be seen in r11 and r12, as is the > original r1 (adjusted by INT_FRAME_SIZE). These are the most important > parts to debugging the issue. > > The original r9-12 and cr0 is lost, which is the main downside. > > kernel BUG at linux/arch/powerpc/kernel/exceptions-64s.S:847! > Oops: Exception in kernel mode, sig: 5 [#1] > BE SMP NR_CPUS=2048 NUMA PowerNV > Modules linked in: > CPU: 0 PID: 1 Comm: swapper/0 Not tainted > NIP: c000000000009108 LR: c000000000cadbcc CTR: c0000000000090f0 > REGS: c0000000fffcbd70 TRAP: 0700 Not tainted > MSR: 9000000000021032 <SF,HV,ME,IR,DR,RI> CR: 28222448 XER: 20040000 > CFAR: c000000000009100 IRQMASK: 0 > GPR00: 000000000000003d fffffffffffffd00 c0000000018cfb00 c0000000f02b3166 > GPR04: fffffffffffffffd 0000000000000007 fffffffffffffffb 0000000000000030 > GPR08: 0000000000000037 0000000028222448 0000000000000000 c000000000ca8de0 > GPR12: 9000000002009032 c000000001ae0000 c000000000010a00 0000000000000000 > GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 > GPR20: c0000000f00322c0 c000000000f85200 0000000000000004 ffffffffffffffff > GPR24: fffffffffffffffe 0000000000000000 0000000000000000 000000000000000a > GPR28: 0000000000000000 0000000000000000 c0000000f02b391c c0000000f02b3167 > NIP [c000000000009108] decrementer_common+0x18/0x160 > LR [c000000000cadbcc] .vsnprintf+0x3ec/0x4f0 > Call Trace: > Instruction dump: > 996d098a 994d098b 38610070 480246ed 48005518 60000000 38200000 718a4000 > 7c2a0b78 3821fd00 41c20008 e82d0970 <0981fd00> f92101a0 f9610170 f9810178 > > Signed-off-by: Nicholas Piggin <[email protected]>
Series applied to powerpc next, thanks. https://git.kernel.org/powerpc/c/0a882e28468f48ab3d9a36dde0a5723ea29ed1ed cheers
