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authorSteven Rostedt (VMware) <rostedt@goodmis.org>2017-09-05 11:32:01 -0400
committerSteven Rostedt (VMware) <rostedt@goodmis.org>2017-09-05 11:54:33 -0400
commit3d9622c12c8873911f4cc0ccdabd0362c2fca06b (patch)
tree8ff2232b40d0329588b1329689b7c5a8ae4b5d20 /kernel
parentedb096e00724f02db5f6ec7900f3bbd465c6c76f (diff)
tracing: Add barrier to trace_printk() buffer nesting modification
trace_printk() uses 4 buffers, one for each context (normal, softirq, irq and NMI), such that it does not need to worry about one context preempting the other. There's a nesting counter that gets incremented to figure out which buffer to use. If the context gets preempted by another context which calls trace_printk() it will increment the counter and use the next buffer, and restore the counter when it is finished. The problem is that gcc may optimize the modification of the buffer nesting counter and it may not be incremented in memory before the buffer is used. If this happens, and the context gets interrupted by another context, it could pick the same buffer and corrupt the one that is being used. Compiler barriers need to be added after the nesting variable is incremented and before it is decremented to prevent usage of the context buffers by more than one context at the same time. Cc: Andy Lutomirski <luto@kernel.org> Cc: stable@vger.kernel.org Fixes: e2ace00117 ("tracing: Choose static tp_printk buffer by explicit nesting count") Hat-tip-to: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/trace/trace.c8
1 files changed, 7 insertions, 1 deletions
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 30338a835a51..78842557eea0 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2802,11 +2802,17 @@ static char *get_trace_buf(void)
if (!buffer || buffer->nesting >= 4)
return NULL;
- return &buffer->buffer[buffer->nesting++][0];
+ buffer->nesting++;
+
+ /* Interrupts must see nesting incremented before we use the buffer */
+ barrier();
+ return &buffer->buffer[buffer->nesting][0];
}
static void put_trace_buf(void)
{
+ /* Don't let the decrement of nesting leak before this */
+ barrier();
this_cpu_dec(trace_percpu_buffer->nesting);
}