1. 21 Jan, 2013 1 commit
    • Steven Rostedt's avatar
      ftrace: Be first to run code modification on modules · c1bf08ac
      Steven Rostedt authored
      If some other kernel subsystem has a module notifier, and adds a kprobe
      to a ftrace mcount point (now that kprobes work on ftrace points),
      when the ftrace notifier runs it will fail and disable ftrace, as well
      as kprobes that are attached to ftrace points.
      
      Here's the error:
      
       WARNING: at kernel/trace/ftrace.c:1618 ftrace_bug+0x239/0x280()
       Hardware name: Bochs
       Modules linked in: fat(+) stap_56d28a51b3fe546293ca0700b10bcb29__8059(F) nfsv4 auth_rpcgss nfs dns_resolver fscache xt_nat iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack lockd sunrpc ppdev parport_pc parport microcode virtio_net i2c_piix4 drm_kms_helper ttm drm i2c_core [last unloaded: bid_shared]
       Pid: 8068, comm: modprobe Tainted: GF            3.7.0-0.rc8.git0.1.fc19.x86_64 #1
       Call Trace:
        [<ffffffff8105e70f>] warn_slowpath_common+0x7f/0xc0
        [<ffffffff81134106>] ? __probe_kernel_read+0x46/0x70
        [<ffffffffa0180000>] ? 0xffffffffa017ffff
        [<ffffffffa0180000>] ? 0xffffffffa017ffff
        [<ffffffff8105e76a>] warn_slowpath_null+0x1a/0x20
        [<ffffffff810fd189>] ftrace_bug+0x239/0x280
        [<ffffffff810fd626>] ftrace_process_locs+0x376/0x520
        [<ffffffff810fefb7>] ftrace_module_notify+0x47/0x50
        [<ffffffff8163912d>] notifier_call_chain+0x4d/0x70
        [<ffffffff810882f8>] __blocking_notifier_call_chain+0x58/0x80
        [<ffffffff81088336>] blocking_notifier_call_chain+0x16/0x20
        [<ffffffff810c2a23>] sys_init_module+0x73/0x220
        [<ffffffff8163d719>] system_call_fastpath+0x16/0x1b
       ---[ end trace 9ef46351e53bbf80 ]---
       ftrace failed to modify [<ffffffffa0180000>] init_once+0x0/0x20 [fat]
        actual: cc:bb:d2:4b:e1
      
      A kprobe was added to the init_once() function in the fat module on load.
      But this happened before ftrace could have touched the code. As ftrace
      didn't run yet, the kprobe system had no idea it was a ftrace point and
      simply added a breakpoint to the code (0xcc in the cc:bb:d2:4b:e1).
      
      Then when ftrace went to modify the location from a call to mcount/fentry
      into a nop, it didn't see a call op, but instead it saw the breakpoint op
      and not knowing what to do with it, ftrace shut itself down.
      
      The solution is to simply give the ftrace module notifier the max priority.
      This should have been done regardless, as the core code ftrace modification
      also happens very early on in boot up. This makes the module modification
      closer to core modification.
      
      Link: http://lkml.kernel.org/r/20130107140333.593683061@goodmis.org
      
      
      
      Cc: stable@vger.kernel.org
      Acked-by: default avatarMasami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
      Reported-by: default avatarFrank Ch. Eigler <fche@redhat.com>
      Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      c1bf08ac
  2. 17 Jan, 2013 2 commits
  3. 16 Jan, 2013 25 commits
  4. 15 Jan, 2013 3 commits
  5. 14 Jan, 2013 9 commits