[Issue]
If one cpu ,which is taking a psinfo->buf_lock,
receive NMI from a panicked cpu via smp_send_stop(),
the panicked cpu hangs up in pstore_dump() called by kmsg_dump(KMSG_DUMP_PANIC)
because the psinfo->buf_lock is taken again in it.
To avoid the deadlock, an easy solution is moving kmsg_dump above
smp_send_stop() in panic path.
But, it is not safe to kick pstore while multiple cpus are running in panic
case,
because they may touch corrupted data/variables and unnecessary failures may
happen.
In that case, we can't guarantee that a panicked cpu can log messages reliably
because it may have harmful effects due to the failures.
[Solution]
This patch skips taking a psinfo->buf_lock when just one cpu is online
because stopped cpus turn to offline via smp_send_stop()
in some architectures like x86, powerpc or arm64.
It may be a hack but solves my concern deadlocking in x86 architecture.
Signed-off-by: Seiji Aguchi <seiji.agu...@hds.com>
---
fs/pstore/platform.c | 14 +++++++++++---
1 files changed, 11 insertions(+), 3 deletions(-)
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index 947fbe0..ca4d2ab 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -107,7 +107,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
unsigned long total = 0;
const char *why;
u64 id;
- unsigned int part = 1;
+ unsigned int part = 1, cpu_num = num_online_cpus();
unsigned long flags = 0;
int is_locked = 0;
int ret;
@@ -118,8 +118,14 @@ static void pstore_dump(struct kmsg_dumper *dumper,
is_locked = spin_trylock(&psinfo->buf_lock);
if (!is_locked)
pr_err("pstore dump routine blocked in NMI, may corrupt
error record\n");
- } else
+ } else if (cpu_num > 1) {
+ /*
+ * Take a spin lock only when multiple cpus are online.
+ */
spin_lock_irqsave(&psinfo->buf_lock, flags);
+ } else
+ local_irq_save(flags);
+
oopscount++;
while (total < kmsg_bytes) {
char *dst;
@@ -146,8 +152,10 @@ static void pstore_dump(struct kmsg_dumper *dumper,
if (in_nmi()) {
if (is_locked)
spin_unlock(&psinfo->buf_lock);
- } else
+ } else if (cpu_num > 1) {
spin_unlock_irqrestore(&psinfo->buf_lock, flags);
+ } else
+ local_irq_restore(flags);
}
static struct kmsg_dumper pstore_dumper = {
-- 1.7.1
--
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