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authorDaniel Thompson <daniel.thompson@linaro.org>2014-11-06 12:41:55 +0000
committerSteven Rostedt <rostedt@goodmis.org>2014-11-13 21:24:24 -0500
commitc270cc75cd22b606c901e606fbb93b002c2a655f (patch)
tree8bc4fe40fa7571f224e1890b7fc7b6e830217a63 /kernel/trace
parent933ff9f20220e1339964c7a76a34ca9aaa4a8c37 (diff)
downloadlinux-c270cc75cd22b606c901e606fbb93b002c2a655f.tar.bz2
tracing: kdb: Fix kernel panic during ftdump
Currently kdb's ftdump command unconditionally crashes due to a null pointer de-reference whenever the command is run. This in turn causes the kernel to panic. The abridged stacktrace (gathered with ARCH=arm) is: --- cut here --- [<c09535ac>] (panic) from [<c02132dc>] (die+0x264/0x440) [<c02132dc>] (die) from [<c0952eb8>] (__do_kernel_fault.part.11+0x74/0x84) [<c0952eb8>] (__do_kernel_fault.part.11) from [<c021f954>] (do_page_fault+0x1d0/0x3c4) [<c021f954>] (do_page_fault) from [<c020846c>] (do_DataAbort+0x48/0xac) [<c020846c>] (do_DataAbort) from [<c0213c58>] (__dabt_svc+0x38/0x60) Exception stack(0xc0deba88 to 0xc0debad0) ba80: e8c29180 00000001 e9854304 e9854300 c0f567d8 c0df2580 baa0: 00000000 00000000 00000000 c0f117b8 c0e3a3c0 c0debb0c 00000000 c0debad0 bac0: 0000672e c02f4d60 60000193 ffffffff [<c0213c58>] (__dabt_svc) from [<c02f4d60>] (kdb_ftdump+0x1e4/0x3d8) [<c02f4d60>] (kdb_ftdump) from [<c02ce328>] (kdb_parse+0x2b8/0x698) [<c02ce328>] (kdb_parse) from [<c02ceef0>] (kdb_main_loop+0x52c/0x784) [<c02ceef0>] (kdb_main_loop) from [<c02d1b0c>] (kdb_stub+0x238/0x490) --- cut here --- The NULL deref occurs due to the initialized use of struct trace_iter's buffer_iter member. This is a regression, albeit a fairly elderly one. It was introduced by commit 6d158a813efc ("tracing: Remove NR_CPUS array from trace_iterator"). This patch solves this by providing a collection of ring_buffer_iter(s) and using this to initialize buffer_iter. Note that static allocation is used solely because the trace_iter itself is also static allocated. Static allocation also means that we have to NULL-ify the pointer during cleanup to avoid use-after-free problems. Link: http://lkml.kernel.org/r/1415277716-19419-2-git-send-email-daniel.thompson@linaro.org Cc: Jason Wessel <jason.wessel@windriver.com> Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace')
-rw-r--r--kernel/trace/trace_kdb.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/kernel/trace/trace_kdb.c b/kernel/trace/trace_kdb.c
index bd90e1b06088..8faa7ce58814 100644
--- a/kernel/trace/trace_kdb.c
+++ b/kernel/trace/trace_kdb.c
@@ -20,10 +20,12 @@ static void ftrace_dump_buf(int skip_lines, long cpu_file)
{
/* use static because iter can be a bit big for the stack */
static struct trace_iterator iter;
+ static struct ring_buffer_iter *buffer_iter[CONFIG_NR_CPUS];
unsigned int old_userobj;
int cnt = 0, cpu;
trace_init_global_iter(&iter);
+ iter.buffer_iter = buffer_iter;
for_each_tracing_cpu(cpu) {
atomic_inc(&per_cpu_ptr(iter.trace_buffer->data, cpu)->disabled);
@@ -86,9 +88,12 @@ out:
atomic_dec(&per_cpu_ptr(iter.trace_buffer->data, cpu)->disabled);
}
- for_each_tracing_cpu(cpu)
- if (iter.buffer_iter[cpu])
+ for_each_tracing_cpu(cpu) {
+ if (iter.buffer_iter[cpu]) {
ring_buffer_read_finish(iter.buffer_iter[cpu]);
+ iter.buffer_iter[cpu] = NULL;
+ }
+ }
}
/*