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authorValentin Schneider <vschneid@redhat.com>2022-06-30 23:32:57 +0100
committerAndrew Morton <akpm@linux-foundation.org>2022-09-11 21:55:06 -0700
commit7bb5da0d490b2d836c5218f5186ee588d2145310 (patch)
tree2b6b1003e79581a22fa0438c40d48e42a645806a
parent9847f21225c4eb0b843cb2b72ed83b32edb1e6f2 (diff)
kexec: turn all kexec_mutex acquisitions into trylocks
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>
-rw-r--r--include/linux/kexec.h2
-rw-r--r--kernel/kexec_core.c12
-rw-r--r--kernel/ksysfs.c7
3 files changed, 15 insertions, 6 deletions
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 13e6c4b58f07..41a686996aaa 100644
--- a/include/linux/kexec.h
+++ b/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
/*
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index acd029b307e4..8fa4eeb95b30 100644
--- a/kernel/kexec_core.c
+++ b/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 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 b1292a57c2a5..65dba9076f31 100644
--- a/kernel/ksysfs.c
+++ b/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,