The patch titled
Subject: kexec: turn all kexec_mutex acquisitions into trylocks
has been added to the -mm mm-nonmm-unstable branch. Its filename is
kexec-turn-all-kexec_mutex-acquisitions-into-trylocks.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kexec-turn-all-kexec_mutex-acquisitions-into-trylocks.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Valentin Schneider <vschneid@xxxxxxxxxx>
Subject: kexec: turn all kexec_mutex acquisitions into trylocks
Date: Thu, 30 Jun 2022 23:32:57 +0100
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@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20220630223258.4144112-2-vschneid@xxxxxxxxxx
Signed-off-by: Valentin Schneider <vschneid@xxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: "Eric W . Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Juri Lelli <jlelli@xxxxxxxxxx>
Cc: Luis Claudio R. Goncalves <lgoncalv@xxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/kexec.h | 2 +-
kernel/kexec_core.c | 12 ++++++++----
kernel/ksysfs.c | 7 ++++++-
3 files changed, 15 insertions(+), 6 deletions(-)
--- a/include/linux/kexec.h~kexec-turn-all-kexec_mutex-acquisitions-into-trylocks
+++ a/include/linux/kexec.h
@@ -427,7 +427,7 @@ extern int kexec_load_disabled;
extern bool kexec_in_progress;
int crash_shrink_memory(unsigned long new_size);
-size_t crash_get_memory_size(void);
+ssize_t crash_get_memory_size(void);
#ifndef arch_kexec_protect_crashkres
/*
--- a/kernel/kexec_core.c~kexec-turn-all-kexec_mutex-acquisitions-into-trylocks
+++ a/kernel/kexec_core.c
@@ -1004,13 +1004,16 @@ 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;
}
@@ -1022,7 +1025,8 @@ int crash_shrink_memory(unsigned long ne
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;
--- a/kernel/ksysfs.c~kexec-turn-all-kexec_mutex-acquisitions-into-trylocks
+++ a/kernel/ksysfs.c
@@ -105,7 +105,12 @@ 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,
_
Patches currently in -mm which might be from vschneid@xxxxxxxxxx are
kexec-turn-all-kexec_mutex-acquisitions-into-trylocks.patch
panic-kexec-make-__crash_kexec-nmi-safe.patch
