Messages in this thread | | | Date | Tue, 25 Aug 2009 16:15:49 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 08/12] add trace events for each syscall entry/exit |
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On Tue, Aug 25, 2009 at 02:50:27PM +0200, Hendrik Brueckner wrote: > On Mon, Aug 10, 2009 at 04:52:47PM -0400, Jason Baron wrote: > > +void ftrace_syscall_enter(struct pt_regs *regs, long id) > > { > > struct syscall_trace_enter *entry; > > struct syscall_metadata *sys_data; > > @@ -150,6 +105,8 @@ void ftrace_syscall_enter(struct pt_regs *regs) > > int syscall_nr; > > > > syscall_nr = syscall_get_nr(current, regs); > > + if (!test_bit(syscall_nr, enabled_enter_syscalls)) > > + return; > > > > sys_data = syscall_nr_to_meta(syscall_nr); > > if (!sys_data) > > > +void ftrace_syscall_exit(struct pt_regs *regs, long ret) > > { > > struct syscall_trace_exit *entry; > > struct syscall_metadata *sys_data; > > @@ -178,6 +135,8 @@ void ftrace_syscall_exit(struct pt_regs *regs) > > int syscall_nr; > > > > syscall_nr = syscall_get_nr(current, regs); > > + if (!test_bit(syscall_nr, enabled_exit_syscalls)) > > + return; > 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.
I wonder if there is any way to identify such situation...?
> > 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>
Yeah, makes sense. Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
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