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Message-Id: <1363257381-15900-47-git-send-email-luis.henriques@canonical.com>
Date: Thu, 14 Mar 2013 10:35:39 +0000
From: Luis Henriques <luis.henriques@...onical.com>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
kernel-team@...ts.ubuntu.com
Cc: Seiji Aguchi <seiji.aguchi@....com>,
Tony Luck <tony.luck@...el.com>,
Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 46/88] pstore: Avoid deadlock in panic and emergency-restart path
3.5.7.8 -stable review patch. If anyone has any objections, please let me know.
------------------
From: Seiji Aguchi <seiji.aguchi@....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@....com>
Acked-by: Don Zickus <dzickus@...hat.com>
Signed-off-by: Tony Luck <tony.luck@...el.com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
fs/pstore/platform.c | 35 +++++++++++++++++++++++++++++------
include/linux/pstore.h | 6 ++++++
2 files changed, 35 insertions(+), 6 deletions(-)
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index 03ce7a9..e1f4f8a 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -88,6 +88,27 @@ static const char *get_reason_str(enum kmsg_dump_reason reason)
}
}
+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
@@ -106,10 +127,12 @@ static void pstore_dump(struct kmsg_dumper *dumper,
why = get_reason_str(reason);
- 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++;
@@ -135,9 +158,9 @@ static void pstore_dump(struct kmsg_dumper *dumper,
total += hsize + len;
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);
}
diff --git a/include/linux/pstore.h b/include/linux/pstore.h
index e1461e1..318cca1 100644
--- a/include/linux/pstore.h
+++ b/include/linux/pstore.h
@@ -54,12 +54,18 @@ struct pstore_info {
#ifdef CONFIG_PSTORE
extern int pstore_register(struct pstore_info *);
+extern bool pstore_cannot_block_path(enum kmsg_dump_reason reason);
#else
static inline int
pstore_register(struct pstore_info *psi)
{
return -ENODEV;
}
+static inline bool
+pstore_cannot_block_path(enum kmsg_dump_reason reason)
+{
+ return false;
+}
#endif
#endif /*_LINUX_PSTORE_H*/
--
1.8.1.2
--
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