tracing: fprobe: use ftrace if CONFIG_DYNAMIC_FTRACE_WITH_ARGS #10110
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For now, fgraph is used for the fprobe, even if we need trace the entry only. However, the performance of ftrace is better than fgraph, and we can use ftrace_ops for this case. Then performance of kprobe-multi increases from 54M to 69M. Before this commit: $ ./benchs/run_bench_trigger.sh kprobe-multi kprobe-multi : 54.663 ± 0.493M/s After this commit: $ ./benchs/run_bench_trigger.sh kprobe-multi kprobe-multi : 69.447 ± 0.143M/s Mitigation is disable during the bench testing above. Link: https://lore.kernel.org/all/[email protected]/ Signed-off-by: Menglong Dong <[email protected]> Signed-off-by: Masami Hiramatsu (Google) <[email protected]>
Signed-off-by: Menglong Dong <[email protected]>
For now, all the kernel functions who are hooked by the fprobe will be added to the hash table "fprobe_ip_table". The key of it is the function address, and the value of it is "struct fprobe_hlist_node". The budget of the hash table is FPROBE_IP_TABLE_SIZE, which is 256. And this means the overhead of the hash table lookup will grow linearly if the count of the functions in the fprobe more than 256. When we try to hook all the kernel functions, the overhead will be huge. Therefore, replace the hash table with rhltable to reduce the overhead. Link: https://lore.kernel.org/all/[email protected]/ Signed-off-by: Menglong Dong <[email protected]> Signed-off-by: Masami Hiramatsu (Google) <[email protected]>
rcu_read_lock() is not needed in fprobe_entry, but rcu_dereference_check() is used in rhltable_lookup(), which causes suspicious RCU usage warning: WARNING: suspicious RCU usage 6.17.0-rc1-00001-gdfe0d675df82 kernel-patches#1 Tainted: G S ----------------------------- include/linux/rhashtable.h:602 suspicious rcu_dereference_check() usage! ...... stack backtrace: CPU: 1 UID: 0 PID: 4652 Comm: ftracetest Tainted: G S Tainted: [S]=CPU_OUT_OF_SPEC, [I]=FIRMWARE_WORKAROUND Hardware name: Dell Inc. OptiPlex 7040/0Y7WYT, BIOS 1.1.1 10/07/2015 Call Trace: <TASK> dump_stack_lvl+0x7c/0x90 lockdep_rcu_suspicious+0x14f/0x1c0 __rhashtable_lookup+0x1e0/0x260 ? __pfx_kernel_clone+0x10/0x10 fprobe_entry+0x9a/0x450 ? __lock_acquire+0x6b0/0xca0 ? find_held_lock+0x2b/0x80 ? __pfx_fprobe_entry+0x10/0x10 ? __pfx_kernel_clone+0x10/0x10 ? lock_acquire+0x14c/0x2d0 ? __might_fault+0x74/0xc0 function_graph_enter_regs+0x2a0/0x550 ? __do_sys_clone+0xb5/0x100 ? __pfx_function_graph_enter_regs+0x10/0x10 ? _copy_to_user+0x58/0x70 ? __pfx_kernel_clone+0x10/0x10 ? __x64_sys_rt_sigprocmask+0x114/0x180 ? __pfx___x64_sys_rt_sigprocmask+0x10/0x10 ? __pfx_kernel_clone+0x10/0x10 ftrace_graph_func+0x87/0xb0 As we discussed in [1], fix this by using guard(rcu)() in fprobe_entry() to protect the rhltable_lookup() and rhl_for_each_entry_rcu() with rcu_read_lock and suppress this warning. Link: https://lore.kernel.org/all/[email protected]/ Link: https://lore.kernel.org/all/[email protected]/ [1] Reported-by: kernel test robot <[email protected]> Closes: https://lore.kernel.org/oe-lkp/[email protected] Fixes: dfe0d675df82 ("tracing: fprobe: use rhltable for fprobe_ip_table") Signed-off-by: Menglong Dong <[email protected]> Signed-off-by: Masami Hiramatsu (Google) <[email protected]>
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