Commit-ID: 7bbee5ca3896f69f09c68be549cb8997abe6bca6
Gitweb: http://git.kernel.org/tip/7bbee5ca3896f69f09c68be549cb8997abe6bca6
Author: Hidehiro Kawai <hidehiro.kawai.ez@xxxxxxxxxxx>
AuthorDate: Mon, 14 Dec 2015 11:19:11 +0100
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Sat, 19 Dec 2015 11:07:01 +0100
kexec: Fix race between panic() and crash_kexec()
Currently, panic() and crash_kexec() can be called at the same time.
For example (x86 case):
CPU 0:
oops_end()
crash_kexec()
mutex_trylock() // acquired
nmi_shootdown_cpus() // stop other CPUs
CPU 1:
panic()
crash_kexec()
mutex_trylock() // failed to acquire
smp_send_stop() // stop other CPUs
infinite loop
If CPU 1 calls smp_send_stop() before nmi_shootdown_cpus(), kdump
fails.
In another case:
CPU 0:
oops_end()
crash_kexec()
mutex_trylock() // acquired
<NMI>
io_check_error()
panic()
crash_kexec()
mutex_trylock() // failed to acquire
infinite loop
Clearly, this is an undesirable result.
To fix this problem, this patch changes crash_kexec() to exclude others
by using the panic_cpu atomic.
Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@xxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Dave Young <dyoung@xxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: HATAYAMA Daisuke <d.hatayama@xxxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: kexec@xxxxxxxxxxxxxxxxxxx
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Cc: Minfei Huang <mnfhuang@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Seth Jennings <sjenning@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: x86-ml <x86@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/20151210014630.25437.94161.stgit@softrs
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
include/linux/kexec.h | 2 ++
kernel/kexec_core.c | 30 +++++++++++++++++++++++++++++-
kernel/panic.c | 8 ++++++--
3 files changed, 37 insertions(+), 3 deletions(-)
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index d140b1e..7b68d27 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -237,6 +237,7 @@ extern int kexec_purgatory_get_set_symbol(struct kimage *image,
unsigned int size, bool get_value);
extern void *kexec_purgatory_get_symbol_addr(struct kimage *image,
const char *name);
+extern void __crash_kexec(struct pt_regs *);
extern void crash_kexec(struct pt_regs *);
int kexec_should_crash(struct task_struct *);
void crash_save_cpu(struct pt_regs *regs, int cpu);
@@ -332,6 +333,7 @@ int __weak arch_kexec_apply_relocations(const Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
#else /* !CONFIG_KEXEC_CORE */
struct pt_regs;
struct task_struct;
+static inline void __crash_kexec(struct pt_regs *regs) { }
static inline void crash_kexec(struct pt_regs *regs) { }
static inline int kexec_should_crash(struct task_struct *p) { return 0; }
#define kexec_in_progress false
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index 11b64a6..c823f30 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -853,7 +853,12 @@ struct kimage *kexec_image;
struct kimage *kexec_crash_image;
int kexec_load_disabled;
-void crash_kexec(struct pt_regs *regs)
+/*
+ * No panic_cpu check version of crash_kexec(). This function is called
+ * only when panic_cpu holds the current CPU number; this is the only CPU
+ * which processes crash_kexec routines.
+ */
+void __crash_kexec(struct pt_regs *regs)
{
/* Take the kexec_mutex here to prevent sys_kexec_load
* running on one cpu from replacing the crash kernel
@@ -876,6 +881,29 @@ void crash_kexec(struct pt_regs *regs)
}
}
+void crash_kexec(struct pt_regs *regs)
+{
+ int old_cpu, this_cpu;
+
+ /*
+ * Only one CPU is allowed to execute the crash_kexec() code as with
+ * panic(). Otherwise parallel calls of panic() and crash_kexec()
+ * may stop each other. To exclude them, we use panic_cpu here too.
+ */
+ this_cpu = raw_smp_processor_id();
+ old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu);
+ if (old_cpu == PANIC_CPU_INVALID) {
+ /* This is the 1st CPU which comes here, so go ahead. */
+ __crash_kexec(regs);
+
+ /*
+ * Reset panic_cpu to allow another panic()/crash_kexec()
+ * call.
+ */
+ atomic_set(&panic_cpu, PANIC_CPU_INVALID);
+ }
+}
+
size_t crash_get_memory_size(void)
{
size_t size = 0;
diff --git a/kernel/panic.c b/kernel/panic.c
index 06f31b49..b333380 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -136,9 +136,11 @@ void panic(const char *fmt, ...)
* everything else.
* If we want to run this after calling panic_notifiers, pass
* the "crash_kexec_post_notifiers" option to the kernel.
+ *
+ * Bypass the panic_cpu check and call __crash_kexec directly.
*/
if (!crash_kexec_post_notifiers)
- crash_kexec(NULL);
+ __crash_kexec(NULL);
/*
* Note smp_send_stop is the usual smp shutdown function, which
@@ -161,9 +163,11 @@ void panic(const char *fmt, ...)
* panic_notifiers and dumping kmsg before kdump.
* Note: since some panic_notifiers can make crashed kernel
* more unstable, it can increase risks of the kdump failure too.
+ *
+ * Bypass the panic_cpu check and call __crash_kexec directly.
*/
if (crash_kexec_post_notifiers)
- crash_kexec(NULL);
+ __crash_kexec(NULL);
bust_spinlocks(0);
--
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