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authorSteven Rostedt (Red Hat) <rostedt@goodmis.org>2016-01-07 23:40:01 +0300
committerSteven Rostedt <rostedt@goodmis.org>2016-01-07 23:40:01 +0300
commitb7ffffbb46f205e7727a18bcc7a46c3c2b534f7c (patch)
tree56f532feb0be642c9e2aa24250430c8c960eed78 /include/linux/ftrace.h
parentc5d641f92c9633f568740332989c067a0ba7d4dc (diff)
downloadlinux-b7ffffbb46f205e7727a18bcc7a46c3c2b534f7c.tar.xz
ftrace: Add infrastructure for delayed enabling of module functions
Qiu Peiyang pointed out that there's a race when enabling function tracing and loading a module. In order to make the modifications of converting nops in the prologue of functions into callbacks, the text needs to be converted from read-only to read-write. When enabling function tracing, the text permission is updated, the functions are modified, and then they are put back. When loading a module, the updates to convert function calls to mcount is done before the module text is set to read-only. But after it is done, the module text is visible by the function tracer. Thus we have the following race: CPU 0 CPU 1 ----- ----- start function tracing set text to read-write load_module add functions to ftrace set module text read-only update all functions to callbacks modify module functions too < Can't it's read-only > When this happens, ftrace detects the issue and disables itself till the next reboot. To fix this, a new DISABLED flag is added for ftrace records, which all module functions get when they are added. Then later, after the module code is all set, the records will have the DISABLED flag cleared, and they will be enabled if any callback wants all functions to be traced. Note, this doesn't add the delay to later. It simply changes the ftrace_module_init() to do both the setting of DISABLED records, and then immediately calls the enable code. This helps with testing this new code as it has the same behavior as previously. Another change will come after this to have the ftrace_module_enable() called after the text is set to read-only. Cc: Qiu Peiyang <peiyangx.qiu@intel.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'include/linux/ftrace.h')
-rw-r--r--include/linux/ftrace.h6
1 files changed, 4 insertions, 2 deletions
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 4736a826baf5..660e7c698f3b 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -357,6 +357,7 @@ bool is_ftrace_trampoline(unsigned long addr);
* REGS - the record wants the function to save regs
* REGS_EN - the function is set up to save regs.
* IPMODIFY - the record allows for the IP address to be changed.
+ * DISABLED - the record is not ready to be touched yet
*
* When a new ftrace_ops is registered and wants a function to save
* pt_regs, the rec->flag REGS is set. When the function has been
@@ -371,10 +372,11 @@ enum {
FTRACE_FL_TRAMP = (1UL << 28),
FTRACE_FL_TRAMP_EN = (1UL << 27),
FTRACE_FL_IPMODIFY = (1UL << 26),
+ FTRACE_FL_DISABLED = (1UL << 25),
};
-#define FTRACE_REF_MAX_SHIFT 26
-#define FTRACE_FL_BITS 6
+#define FTRACE_REF_MAX_SHIFT 25
+#define FTRACE_FL_BITS 7
#define FTRACE_FL_MASKED_BITS ((1UL << FTRACE_FL_BITS) - 1)
#define FTRACE_FL_MASK (FTRACE_FL_MASKED_BITS << FTRACE_REF_MAX_SHIFT)
#define FTRACE_REF_MAX ((1UL << FTRACE_REF_MAX_SHIFT) - 1)