Re: [Crash-utility] Unable to switch stack frames while using crash
----- Original Message -----
First I would update your crash utility so that you have the
exception
frame dump that was a result of the page fault, because it's possible that
the tty structure pointer is in the register dump. But anyway, without
knowing the kernel version, it's hard to pinpoint exactly which instruction
in n_tty_read() generated the page fault. Was the bad address generated
because the tty structure pointer was NULL? And again, with an updated
crash utility, you'll get more information w/respect to the register
contents at the time of the page fault, and also you might get some help
finding it with "bt -F". I'm not sure where the tty structure gets
allocated from -- is it statically-allocated, or is it allocated from
one of the "size-xxx" slab caches, etc...
BTW, looking at the other guy's report, whose backtrace did contain
the page fault exception frame, you can see that the page fault was
generated upon the execution of the instruction at ffffffff811f03b3,
which is n_tty_read+1420:
...
#9 [ffff88031ce75cf0] page_fault at ffffffff812d7425
[exception RIP: n_tty_read+1420]
RIP: ffffffff811f03b3 RSP: ffff88031ce75da8 RFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8802cbd54a68 RCX: 000000000061c044
RDX: 0000000000000005 RSI: ffff88031ce75e87 RDI: ffff8802cbd54d1c
RBP: ffff88031ce75eb8 R8: 0000000000000000 R9: 0000000000000000
R10: 0000000000616680 R11: 0000000000000246 R12: 000000000061c044
R13: ffff8802cbd54800 R14: 0000000000000000 R15: 7fffffffffffffff
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
#10 [ffff88031ce75ec0] tty_read at ffffffff811ebf7e
...
To find out the line of code that generated the page fault, enter this:
crash> dis -rl n_tty_read+1420
The disassembly will start at the beginning of n_tty_read() and stop at
the instruction above that actually caused the page fault, and you will
also see the source-file/line-number information above that.
I checked a few sample kernels, but none of them seem to have a fault-able
instruction exactly at the exception RIP of n_tty_read+1420, but I'm sure
that if you look at your particular kernel source tree, it will make sense.
Dave