From: Valentin Schneider vschneid@redhat.com

commit 7bb5da0d490b2d836c5218f5186ee588d2145310 upstream.

Patch series "kexec, panic: Making crash_kexec() NMI safe", v4.

This patch (of 2):

Most acquistions of kexec_mutex are done via mutex_trylock() - those were a direct "translation" from:

8c5a1cf0ad3a ("kexec: use a mutex for locking rather than xchg()")

there have however been two additions since then that use mutex_lock(): crash_get_memory_size() and crash_shrink_memory().

A later commit will replace said mutex with an atomic variable, and locking operations will become atomic_cmpxchg(). Rather than having those mutex_lock() become while (atomic_cmpxchg(&lock, 0, 1)), turn them into trylocks that can return -EBUSY on acquisition failure.

This does halve the printable size of the crash kernel, but that's still neighbouring 2G for 32bit kernels which should be ample enough.

Link: https://lkml.kernel.org/r/20220630223258.4144112-1-vschneid@redhat.com Link: https://lkml.kernel.org/r/20220630223258.4144112-2-vschneid@redhat.com Signed-off-by: Valentin Schneider vschneid@redhat.com Cc: Arnd Bergmann arnd@arndb.de Cc: "Eric W . Biederman" ebiederm@xmission.com Cc: Juri Lelli jlelli@redhat.com Cc: Luis Claudio R. Goncalves lgoncalv@redhat.com Cc: Miaohe Lin linmiaohe@huawei.com Cc: Petr Mladek pmladek@suse.com Cc: Sebastian Andrzej Siewior bigeasy@linutronix.de Cc: Thomas Gleixner tglx@linutronix.de Cc: Baoquan He bhe@redhat.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Cc: stable@vger.kernel.org # v5.15+ Signed-off-by: Wen Yang wenyang.linux@foxmail.com --- include/linux/kexec.h | 2 +- kernel/kexec_core.c | 12 ++++++++---- kernel/ksysfs.c | 7 ++++++- 3 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h index cf042d41c87b..88c289ce3039 100644 --- a/include/linux/kexec.h +++ b/include/linux/kexec.h @@ -390,8 +390,8 @@ extern note_buf_t __percpu *crash_notes; extern bool kexec_in_progress;

int crash_shrink_memory(unsigned long new_size); -size_t crash_get_memory_size(void); void crash_free_reserved_phys_range(unsigned long begin, unsigned long end); +ssize_t crash_get_memory_size(void);

void arch_kexec_protect_crashkres(void); void arch_kexec_unprotect_crashkres(void); diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c index 5a5d192a89ac..a101d2b77936 100644 --- a/kernel/kexec_core.c +++ b/kernel/kexec_core.c @@ -989,13 +989,16 @@ void crash_kexec(struct pt_regs *regs) } }

-size_t crash_get_memory_size(void) +ssize_t crash_get_memory_size(void) { - size_t size = 0; + ssize_t size = 0; + + if (!mutex_trylock(&kexec_mutex)) + return -EBUSY;

- mutex_lock(&kexec_mutex); if (crashk_res.end != crashk_res.start) size = resource_size(&crashk_res); + mutex_unlock(&kexec_mutex); return size; } @@ -1016,7 +1019,8 @@ int crash_shrink_memory(unsigned long new_size) unsigned long old_size; struct resource *ram_res;

- mutex_lock(&kexec_mutex); + if (!mutex_trylock(&kexec_mutex)) + return -EBUSY;

if (kexec_crash_image) { ret = -ENOENT; diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c index 35859da8bd4f..e20c19e3ba49 100644 --- a/kernel/ksysfs.c +++ b/kernel/ksysfs.c @@ -106,7 +106,12 @@ KERNEL_ATTR_RO(kexec_crash_loaded); static ssize_t kexec_crash_size_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) { - return sprintf(buf, "%zu\n", crash_get_memory_size()); + ssize_t size = crash_get_memory_size(); + + if (size < 0) + return size; + + return sprintf(buf, "%zd\n", size); } static ssize_t kexec_crash_size_store(struct kobject *kobj, struct kobj_attribute *attr,