lkml.org 
[lkml]   [2013]   [Mar]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[ 129/153] pstore: Avoid deadlock in panic and emergency-restart path
3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Seiji Aguchi <seiji.aguchi@hds.com>

commit 9f244e9cfd70c7c0f82d3c92ce772ab2a92d9f64 upstream.

[Issue]

When pstore is in panic and emergency-restart paths, it may be blocked
in those paths because it simply takes spin_lock.

This is an example scenario which pstore may hang up in a panic path:

- cpuA grabs psinfo->buf_lock
- cpuB panics and calls smp_send_stop
- smp_send_stop sends IRQ to cpuA
- after 1 second, cpuB gives up on cpuA and sends an NMI instead
- cpuA is now in an NMI handler while still holding buf_lock
- cpuB is deadlocked

This case may happen if a firmware has a bug and
cpuA is stuck talking with it more than one second.

Also, this is a similar scenario in an emergency-restart path:

- cpuA grabs psinfo->buf_lock and stucks in a firmware
- cpuB kicks emergency-restart via either sysrq-b or hangcheck timer.
And then, cpuB is deadlocked by taking psinfo->buf_lock again.

[Solution]

This patch avoids the deadlocking issues in both panic and emergency_restart
paths by introducing a function, is_non_blocking_path(), to check if a cpu
can be blocked in current path.

With this patch, pstore is not blocked even if another cpu has
taken a spin_lock, in those paths by changing from spin_lock_irqsave
to spin_trylock_irqsave.

In addition, according to a comment of emergency_restart() in kernel/sys.c,
spin_lock shouldn't be taken in an emergency_restart path to avoid
deadlock. This patch fits the comment below.

<snip>
/**
* emergency_restart - reboot the system
*
* Without shutting down any hardware or taking any locks
* reboot the system. This is called when we know we are in
* trouble so this is our best effort to reboot. This is
* safe to call in interrupt context.
*/
void emergency_restart(void)
<snip>

Signed-off-by: Seiji Aguchi <seiji.aguchi@hds.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
[bwh: Backported to 3.2:
- Adjust context
- Add #include <linux/kmsg_dump.h>]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -72,6 +72,27 @@ static char *reason_str[] = {
"Oops", "Panic", "Kexec", "Restart", "Halt", "Poweroff", "Emergency"
};

+bool pstore_cannot_block_path(enum kmsg_dump_reason reason)
+{
+ /*
+ * In case of NMI path, pstore shouldn't be blocked
+ * regardless of reason.
+ */
+ if (in_nmi())
+ return true;
+
+ switch (reason) {
+ /* In panic case, other cpus are stopped by smp_send_stop(). */
+ case KMSG_DUMP_PANIC:
+ /* Emergency restart shouldn't be blocked by spin lock. */
+ case KMSG_DUMP_EMERG:
+ return true;
+ default:
+ return false;
+ }
+}
+EXPORT_SYMBOL_GPL(pstore_cannot_block_path);
+
/*
* callback from kmsg_dump. (s2,l2) has the most recently
* written bytes, older bytes are in (s1,l1). Save as much
@@ -97,10 +118,12 @@ static void pstore_dump(struct kmsg_dump
else
why = "Unknown";

- if (in_nmi()) {
- is_locked = spin_trylock(&psinfo->buf_lock);
- if (!is_locked)
- pr_err("pstore dump routine blocked in NMI, may corrupt error record\n");
+ if (pstore_cannot_block_path(reason)) {
+ is_locked = spin_trylock_irqsave(&psinfo->buf_lock, flags);
+ if (!is_locked) {
+ pr_err("pstore dump routine blocked in %s path, may corrupt error record\n"
+ , in_nmi() ? "NMI" : why);
+ }
} else
spin_lock_irqsave(&psinfo->buf_lock, flags);
oopscount++;
@@ -131,9 +154,9 @@ static void pstore_dump(struct kmsg_dump
total += l1_cpy + l2_cpy;
part++;
}
- if (in_nmi()) {
+ if (pstore_cannot_block_path(reason)) {
if (is_locked)
- spin_unlock(&psinfo->buf_lock);
+ spin_unlock_irqrestore(&psinfo->buf_lock, flags);
} else
spin_unlock_irqrestore(&psinfo->buf_lock, flags);
}
--- a/include/linux/pstore.h
+++ b/include/linux/pstore.h
@@ -22,6 +22,8 @@
#ifndef _LINUX_PSTORE_H
#define _LINUX_PSTORE_H

+#include <linux/kmsg_dump.h>
+
/* types */
enum pstore_type_id {
PSTORE_TYPE_DMESG = 0,
@@ -50,6 +52,7 @@ struct pstore_info {

#ifdef CONFIG_PSTORE
extern int pstore_register(struct pstore_info *);
+extern bool pstore_cannot_block_path(enum kmsg_dump_reason reason);
extern int pstore_write(enum pstore_type_id type, char *buf, size_t size);
#else
static inline int
@@ -57,6 +60,11 @@ pstore_register(struct pstore_info *psi)
{
return -ENODEV;
}
+static inline bool
+pstore_cannot_block_path(enum kmsg_dump_reason reason)
+{
+ return false;
+}
static inline int
pstore_write(enum pstore_type_id type, char *buf, size_t size)
{



\
 
 \ /
  Last update: 2013-03-04 06:01    [W:0.572 / U:0.484 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site