4.14-stable review patch. If anyone has any objections, please let me know.
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From: Pratyush Anand panand@redhat.com
[ Upstream commit 9f416319f40cd857d2bb517630e5855a905ef3fb ]
do_task_stat() calls get_wchan(), which further does unwind_frame(). unwind_frame() restores frame->pc to original value in case function graph tracer has modified a return address (LR) in a stack frame to hook a function return. However, if function graph tracer has hit a filtered function, then we can't unwind it as ftrace_push_return_trace() has biased the index(frame->graph) with a 'huge negative' offset(-FTRACE_NOTRACE_DEPTH).
Moreover, arm64 stack walker defines index(frame->graph) as unsigned int, which can not compare a -ve number.
Similar problem we can have with calling of walk_stackframe() from save_stack_trace_tsk() or dump_backtrace().
This patch fixes unwind_frame() to test the index for -ve value and restore index accordingly before we can restore frame->pc.
Reproducer:
cd /sys/kernel/debug/tracing/ echo schedule > set_graph_notrace echo 1 > options/display-graph echo wakeup > current_tracer ps -ef | grep -i agent
Above commands result in: Unable to handle kernel paging request at virtual address ffff801bd3d1e000 pgd = ffff8003cbe97c00 [ffff801bd3d1e000] *pgd=0000000000000000, *pud=0000000000000000 Internal error: Oops: 96000006 [#1] SMP [...] CPU: 5 PID: 11696 Comm: ps Not tainted 4.11.0+ #33 [...] task: ffff8003c21ba000 task.stack: ffff8003cc6c0000 PC is at unwind_frame+0x12c/0x180 LR is at get_wchan+0xd4/0x134 pc : [<ffff00000808892c>] lr : [<ffff0000080860b8>] pstate: 60000145 sp : ffff8003cc6c3ab0 x29: ffff8003cc6c3ab0 x28: 0000000000000001 x27: 0000000000000026 x26: 0000000000000026 x25: 00000000000012d8 x24: 0000000000000000 x23: ffff8003c1c04000 x22: ffff000008c83000 x21: ffff8003c1c00000 x20: 000000000000000f x19: ffff8003c1bc0000 x18: 0000fffffc593690 x17: 0000000000000000 x16: 0000000000000001 x15: 0000b855670e2b60 x14: 0003e97f22cf1d0f x13: 0000000000000001 x12: 0000000000000000 x11: 00000000e8f4883e x10: 0000000154f47ec8 x9 : 0000000070f367c0 x8 : 0000000000000000 x7 : 00008003f7290000 x6 : 0000000000000018 x5 : 0000000000000000 x4 : ffff8003c1c03cb0 x3 : ffff8003c1c03ca0 x2 : 00000017ffe80000 x1 : ffff8003cc6c3af8 x0 : ffff8003d3e9e000
Process ps (pid: 11696, stack limit = 0xffff8003cc6c0000) Stack: (0xffff8003cc6c3ab0 to 0xffff8003cc6c4000) [...] [<ffff00000808892c>] unwind_frame+0x12c/0x180 [<ffff000008305008>] do_task_stat+0x864/0x870 [<ffff000008305c44>] proc_tgid_stat+0x3c/0x48 [<ffff0000082fde0c>] proc_single_show+0x5c/0xb8 [<ffff0000082b27e0>] seq_read+0x160/0x414 [<ffff000008289e6c>] __vfs_read+0x58/0x164 [<ffff00000828b164>] vfs_read+0x88/0x144 [<ffff00000828c2e8>] SyS_read+0x60/0xc0 [<ffff0000080834a0>] __sys_trace_return+0x0/0x4
Fixes: 20380bb390a4 (arm64: ftrace: fix a stack tracer's output under function graph tracer) Signed-off-by: Pratyush Anand panand@redhat.com Signed-off-by: Jerome Marchand jmarchan@redhat.com [catalin.marinas@arm.com: replace WARN_ON with WARN_ON_ONCE] Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/include/asm/stacktrace.h | 2 +- arch/arm64/kernel/stacktrace.c | 5 +++++ arch/arm64/kernel/time.c | 2 +- 3 files changed, 7 insertions(+), 2 deletions(-)
--- a/arch/arm64/include/asm/stacktrace.h +++ b/arch/arm64/include/asm/stacktrace.h @@ -27,7 +27,7 @@ struct stackframe { unsigned long fp; unsigned long pc; #ifdef CONFIG_FUNCTION_GRAPH_TRACER - unsigned int graph; + int graph; #endif };
--- a/arch/arm64/kernel/stacktrace.c +++ b/arch/arm64/kernel/stacktrace.c @@ -59,6 +59,11 @@ int notrace unwind_frame(struct task_str #ifdef CONFIG_FUNCTION_GRAPH_TRACER if (tsk->ret_stack && (frame->pc == (unsigned long)return_to_handler)) { + if (WARN_ON_ONCE(frame->graph == -1)) + return -EINVAL; + if (frame->graph < -1) + frame->graph += FTRACE_NOTRACE_DEPTH; + /* * This is a case where function graph tracer has * modified a return address (LR) in a stack frame --- a/arch/arm64/kernel/time.c +++ b/arch/arm64/kernel/time.c @@ -52,7 +52,7 @@ unsigned long profile_pc(struct pt_regs frame.fp = regs->regs[29]; frame.pc = regs->pc; #ifdef CONFIG_FUNCTION_GRAPH_TRACER - frame.graph = -1; /* no task info */ + frame.graph = current->curr_ret_stack; #endif do { int ret = unwind_frame(NULL, &frame);