[PATCHv2] tracing: handle atomic context in graph_trace_open()

From: Rabin Vincent
Date: Mon Apr 13 2015 - 16:30:25 EST

graph_trace_open() can be called in atomic context from ftrace_dump().
Use GFP_ATOMIC for the memory allocations when that's the case, in order
to avoid the following splat.

BUG: sleeping function called from invalid context at mm/slab.c:2849
in_atomic(): 1, irqs_disabled(): 128, pid: 0, name: swapper/0
[<8004dc94>] (__might_sleep) from [<801371f4>] (kmem_cache_alloc_trace+0x160/0x238)
r7:87800040 r6:000080d0 r5:810d16e8 r4:000080d0
[<80137094>] (kmem_cache_alloc_trace) from [<800cbd60>] (graph_trace_open+0x30/0xd0)
r10:00000100 r9:809171a8 r8:00008e28 r7:810d16f0 r6:00000001 r5:810d16e8
[<800cbd30>] (graph_trace_open) from [<800c79c4>] (trace_init_global_iter+0x50/0x9c)
r8:00008e28 r7:808c853c r6:00000001 r5:810d16e8 r4:810d16f0 r3:800cbd30
[<800c7974>] (trace_init_global_iter) from [<800c7aa0>] (ftrace_dump+0x90/0x2ec)
r4:810d2580 r3:00000000
[<800c7a10>] (ftrace_dump) from [<80414b2c>] (sysrq_ftrace_dump+0x1c/0x20)
r10:00000100 r9:809171a8 r8:808f6e7c r7:00000001 r6:00000007 r5:0000007a
[<80414b10>] (sysrq_ftrace_dump) from [<800169b8>] (return_to_handler+0x0/0x18)
[<80415498>] (__handle_sysrq) from [<800169b8>] (return_to_handler+0x0/0x18)
r8:808c8100 r7:808c8444 r6:00000101 r5:00000010 r4:84eb3210
[<80415668>] (handle_sysrq) from [<800169b8>] (return_to_handler+0x0/0x18)
[<8042a760>] (pl011_int) from [<800169b8>] (return_to_handler+0x0/0x18)
r10:809171bc r9:809171a8 r8:00000001 r7:00000026 r6:808c6000 r5:84f01e60
[<8007782c>] (handle_irq_event_percpu) from [<80077b44>] (handle_irq_event+0x4c/0x6c)
r10:808c7ef0 r9:87283e00 r8:00000001 r7:00000000 r6:8454fe00 r5:84f01e60
[<80077af8>] (handle_irq_event) from [<8007aa28>] (handle_fasteoi_irq+0xf0/0x1ac)
r6:808f52a4 r5:84f01e60 r4:84f01e00 r3:00000000
[<8007a938>] (handle_fasteoi_irq) from [<80076dc0>] (generic_handle_irq+0x3c/0x4c)
r6:00000026 r5:00000000 r4:00000026 r3:8007a938
[<80076d84>] (generic_handle_irq) from [<80077128>] (__handle_domain_irq+0x8c/0xfc)
r4:808c1e38 r3:0000002e
[<8007709c>] (__handle_domain_irq) from [<800087b8>] (gic_handle_irq+0x34/0x6c)
r10:80917748 r9:00000001 r8:88802100 r7:808c7ef0 r6:808c8fb0 r5:00000015
r4:8880210c r3:808c7ef0
[<80008784>] (gic_handle_irq) from [<80014044>] (__irq_svc+0x44/0x7c)

Signed-off-by: Rabin Vincent <rabin@xxxxxx>
v2: add comment, use appropriate gfp depending on context

kernel/trace/trace_functions_graph.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 2d25ad1..b6fce36 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -1309,15 +1309,19 @@ void graph_trace_open(struct trace_iterator *iter)
/* pid and depth on the last trace processed */
struct fgraph_data *data;
+ gfp_t gfpflags;
int cpu;

iter->private = NULL;

- data = kzalloc(sizeof(*data), GFP_KERNEL);
+ /* We can be called in atomic context via ftrace_dump() */
+ gfpflags = (in_atomic() || irqs_disabled()) ? GFP_ATOMIC : GFP_KERNEL;
+ data = kzalloc(sizeof(*data), gfpflags);
if (!data)
goto out_err;

- data->cpu_data = alloc_percpu(struct fgraph_cpu_data);
+ data->cpu_data = alloc_percpu_gfp(struct fgraph_cpu_data, gfpflags);
if (!data->cpu_data)
goto out_err_free;


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