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authorSteven Rostedt <srostedt@redhat.com>2009-02-19 13:32:57 -0500
committerSteven Rostedt <srostedt@redhat.com>2009-02-20 14:30:18 -0500
commit90c7ac49aa819feb9433b5310089fca6399881c0 (patch)
tree91c5eb0b7379d980eaa68e19073b9552e5fc93e2
parent16239630974516a8879a3695ee9b4dc661f79f96 (diff)
ftrace: immediately stop code modification if failure is detected
Impact: fix to prevent NMI lockup If the page fault handler produces a WARN_ON in the modifying of text, and the system is setup to have a high frequency of NMIs, we can lock up the system on a failure to modify code. The modifying of code with NMIs allows all NMIs to modify the code if it is about to run. This prevents a modifier on one CPU from modifying code running in NMI context on another CPU. The modifying is done through stop_machine, so only NMIs must be considered. But if the write causes the page fault handler to produce a warning, the print can slow it down enough that as soon as it is done it will take another NMI before going back to the process context. The new NMI will perform the write again causing another print and this will hang the box. This patch turns off the writing as soon as a failure is detected and does not wait for it to be turned off by the process context. This will keep NMIs from getting stuck in this back and forth of print outs. Signed-off-by: Steven Rostedt <srostedt@redhat.com>
-rw-r--r--arch/x86/kernel/ftrace.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 77857d4f7d0..c56d7389432 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -124,6 +124,10 @@ static void ftrace_mod_code(void)
*/
mod_code_status = probe_kernel_write(mod_code_ip, mod_code_newcode,
MCOUNT_INSN_SIZE);
+
+ /* if we fail, then kill any new writers */
+ if (mod_code_status)
+ mod_code_write = 0;
}
void ftrace_nmi_enter(void)