In the Linux kernel, the following vulnerability has been resolved: tracing: Fix warning in tracebufferedeventdisable() Warning happened in tracebufferedeventdisable() at WARNONONCE(!tracebufferedeventref) Call Trace: ? _warn+0xa5/0x1b0 ? tracebufferedeventdisable+0x189/0x1b0 _ftraceeventenabledisable+0x19e/0x3e0 freeprobedata+0x3b/0xa0 unregisterftracefunctionprobefunc+0x6b8/0x800 eventenablefunc+0x2f0/0x3d0 ftraceprocessregex.isra.0+0x12d/0x1b0 ftracefilterwrite+0xe6/0x140 vfswrite+0x1c9/0x6f0 [...] The cause of the warning is in _ftraceeventenabledisable(), tracebufferedeventenable() was called once while tracebufferedeventdisable() was called twice. Reproduction script show as below, for analysis, see the comments: #!/bin/bash cd /sys/kernel/tracing/ # 1. Register a 'disable_event' command, then: # 1) SOFT_DISABLED_BIT was set; # 2) trace_buffered_event_enable() was called first time; echo 'cmdline_proc_show:disable_event:initcall:initcall_finish' > \ set_ftrace_filter # 2. Enable the event registered, then: # 1) SOFT_DISABLED_BIT was cleared; # 2) trace_buffered_event_disable() was called first time; echo 1 > events/initcall/initcall_finish/enable # 3. Try to call into cmdline_proc_show(), then SOFT_DISABLED_BIT was # set again!!! cat /proc/cmdline # 4. Unregister the 'disable_event' command, then: # 1) SOFT_DISABLED_BIT was cleared again; # 2) trace_buffered_event_disable() was called second time!!! echo '!cmdline_proc_show:disable_event:initcall:initcall_finish' > \ set_ftrace_filter To fix it, IIUC, we can change to call tracebufferedeventenable() at fist time soft-mode enabled, and call tracebufferedeventdisable() at last time soft-mode disabled.