Messages in this thread Patch in this message | | | Subject | [V4 PATCH 3/4] kexec: Fix race between panic() and crash_kexec() called directly | From | Hidehiro Kawai <> | Date | Fri, 25 Sep 2015 20:28:09 +0900 |
| |
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 atomic_t panic_cpu.
V4: - Use new __crash_kexec(), no exclusion check version of crash_kexec(), instead of checking if panic_cpu is the current cpu or not
V2: - Use atomic_cmpxchg() instead of spin_trylock() on panic_lock to exclude concurrent accesses - Don't introduce no-lock version of crash_kexec()
Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com> Cc: Eric Biederman <ebiederm@xmission.com> Cc: Vivek Goyal <vgoyal@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Michal Hocko <mhocko@kernel.org> --- include/linux/kexec.h | 1 + kernel/kexec_core.c | 26 +++++++++++++++++++++++++- kernel/panic.c | 4 ++-- 3 files changed, 28 insertions(+), 3 deletions(-)
diff --git a/include/linux/kexec.h b/include/linux/kexec.h index d140b1e..f0cd2fa 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); diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c index 201b453..4edb20a 100644 --- a/kernel/kexec_core.c +++ b/kernel/kexec_core.c @@ -853,7 +853,8 @@ int kimage_load_segment(struct kimage *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 */ +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 +877,29 @@ 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, -1, this_cpu); + if (old_cpu == -1) { + /* 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_xchg(&panic_cpu, -1); + } +} + size_t crash_get_memory_size(void) { size_t size = 0; diff --git a/kernel/panic.c b/kernel/panic.c index cddbfe0..994be45 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -137,7 +137,7 @@ void panic(const char *fmt, ...) * the "crash_kexec_post_notifiers" option to the kernel. */ if (!crash_kexec_post_notifiers) - crash_kexec(NULL); + __crash_kexec(NULL); /* * Note smp_send_stop is the usual smp shutdown function, which @@ -162,7 +162,7 @@ void panic(const char *fmt, ...) * more unstable, it can increase risks of the kdump failure too. */ if (crash_kexec_post_notifiers) - crash_kexec(NULL); + __crash_kexec(NULL); bust_spinlocks(0);
| |