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authorHidehiro Kawai <hidehiro.kawai.ez@hitachi.com>2015-12-14 11:19:11 +0100
committerThomas Gleixner <tglx@linutronix.de>2015-12-19 11:07:01 +0100
commit7bbee5ca3896f69f09c68be549cb8997abe6bca6 (patch)
treeaa2ffe78b5f70617f6fec0da5d3075962bf392d2 /kernel/kexec_core.c
parent58c5661f2144c089bbc2e5d87c9ec1dc1d2964fe (diff)
downloadlinux-7bbee5ca3896f69f09c68be549cb8997abe6bca6.tar.bz2
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@hitachi.com> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Baoquan He <bhe@redhat.com> Cc: Dave Young <dyoung@redhat.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: kexec@lists.infradead.org Cc: linux-doc@vger.kernel.org Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Cc: Minfei Huang <mnfhuang@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Seth Jennings <sjenning@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vitaly Kuznetsov <vkuznets@redhat.com> Cc: Vivek Goyal <vgoyal@redhat.com> Cc: x86-ml <x86@kernel.org> Link: http://lkml.kernel.org/r/20151210014630.25437.94161.stgit@softrs Signed-off-by: Borislav Petkov <bp@suse.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/kexec_core.c')
-rw-r--r--kernel/kexec_core.c30
1 files changed, 29 insertions, 1 deletions
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index 11b64a63c0f8..c823f3001e12 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;