lkml.org 
[lkml]   [2009]   [Aug]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 08/12] add trace events for each syscall entry/exit
    On Tue, Aug 25, 2009 at 11:40:21PM +0200, Frederic Weisbecker wrote:
    > On Tue, Aug 25, 2009 at 02:50:27PM +0200, Hendrik Brueckner wrote:
    > > Most arch syscall_get_nr() implementations returns -1 if the syscall
    > > number is not valid. Accessing the bit field without a check might
    > > result in a kernel oops (at least I saw it on s390 for ftrace selftest).
    > >
    > > Before this change, this problem did not occur, because the invalid
    > > syscall number (-1) caused syscall_nr_to_meta() to return NULL.
    > >
    > > There are at least two scenarios where syscall_get_nr() can return -1:
    > >
    > > 1. For example, ptrace stores an invalid syscall number, and thus,
    > > tracing code resets it.
    > > (see do_syscall_trace_enter in arch/s390/kernel/ptrace.c)
    > >
    > > 2. The syscall_regfunc() (kernel/tracepoint.c) sets the TIF_SYSCALL_FTRACE
    > > (now: TIF_SYSCALL_TRACEPOINT) flag for all threads which includes
    > > kernel threads.
    > > However, the ftrace selftest triggers a kernel oops when testing syscall
    > > trace points:
    > > - The kernel thread is started as ususal (do_fork()),
    > > - tracing code sets TIF_SYSCALL_FTRACE,
    > > - the ret_from_fork() function is triggered and starts
    > > ftrace_syscall_exit() with an invalid syscall number.
    > >
    > > To avoid these scenarios, I suggest to check the syscall_nr.
    > >
    > > For instance, the ftrace selftest fails for s390 (with config option
    > > CONFIG_FTRACE_SYSCALLS set) and produces the following kernel oops.
    > >
    > > Unable to handle kernel pointer dereference at virtual kernel address 2000000000
    > >
    > > Oops: 0038 [#1] PREEMPT SMP
    > > Modules linked in:
    > > CPU: 0 Not tainted 2.6.31-rc6-next-20090819-dirty #18
    > > Process kthreadd (pid: 818, task: 000000003ea207e8, ksp: 000000003e813eb8)
    > > Krnl PSW : 0704100180000000 00000000000ea54c (ftrace_syscall_exit+0x58/0xdc)
    > > R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:0 CC:1 PM:0 EA:3
    > > Krnl GPRS: 0000000000000000 00000000000e0000 ffffffffffffffff 20000000008c2650
    > > 0000000000000007 0000000000000000 0000000000000000 0000000000000000
    > > 0000000000000000 0000000000000000 ffffffffffffffff 000000003e813d78
    > > 000000003e813f58 0000000000505ba8 000000003e813e18 000000003e813d78
    > > Krnl Code: 00000000000ea540: e330d0000008 ag %r3,0(%r13)
    > > 00000000000ea546: a7480007 lhi %r4,7
    > > 00000000000ea54a: 1442 nr %r4,%r2
    > > >00000000000ea54c: e31030000090 llgc %r1,0(%r3)
    > > 00000000000ea552: 5410d008 n %r1,8(%r13)
    > > 00000000000ea556: 8a104000 sra %r1,0(%r4)
    > > 00000000000ea55a: 5410d00c n %r1,12(%r13)
    > > 00000000000ea55e: 1211 ltr %r1,%r1
    > > Call Trace:
    > > ([<0000000000000000>] 0x0)
    > > [<000000000001fa22>] do_syscall_trace_exit+0x132/0x18c
    > > [<000000000002d0c4>] sysc_return+0x0/0x8
    > > [<000000000001c738>] kernel_thread_starter+0x0/0xc
    > > Last Breaking-Event-Address:
    > > [<00000000000ea51e>] ftrace_syscall_exit+0x2a/0xdc
    > >
    > > Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
    >
    >
    >
    > I'm queueing this one for .32
    >
    > Thanks.
    >


    Btw it would be nice to have an ack from s390 maintainers.
    Martin, Heiko, no problem with this patch?



    \
     
     \ /
      Last update: 2009-08-26 00:11    [W:0.032 / U:61.044 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site