sysfs: crash debugging

Print the name of the last-accessed sysfs file when we oops, to help track
down oopses which occur in sysfs store/read handlers.  Because these oopses
tend to not leave any trace of the offending code in the stack traces.

Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

4 files changed, 23 insertions, 0 deletions

diff --git a/arch/x86/kernel/dumpstack_32.c b/arch/x86/kernel/dumpstack_32.c
index 201ee359a1a9..1a78180f08d3 100644
--- a/arch/x86/kernel/dumpstack_32.c
+++ b/arch/x86/kernel/dumpstack_32.c
@@ -13,6 +13,7 @@
 #include <linux/kexec.h>
 #include <linux/bug.h>
 #include <linux/nmi.h>
+#include <linux/sysfs.h>
 
 #include <asm/stacktrace.h>
 
@@ -343,6 +344,7 @@ int __kprobes __die(const char *str, struct pt_regs *regs, long err)
         printk("DEBUG_PAGEALLOC");
 #endif
         printk("\n");
+        sysfs_printk_last_file();
         if (notify_die(DIE_OOPS, str, regs, err,
                         current->thread.trap_no, SIGSEGV) == NOTIFY_STOP)
                 return 1;
diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 086cc8118e39..96a5db7da8a7 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -13,6 +13,7 @@
 #include <linux/kexec.h>
 #include <linux/bug.h>
 #include <linux/nmi.h>
+#include <linux/sysfs.h>
 
 #include <asm/stacktrace.h>
 
@@ -489,6 +490,7 @@ int __kprobes __die(const char *str, struct pt_regs *regs, long err)
         printk("DEBUG_PAGEALLOC");
 #endif
         printk("\n");
+        sysfs_printk_last_file();
         if (notify_die(DIE_OOPS, str, regs, err,
                         current->thread.trap_no, SIGSEGV) == NOTIFY_STOP)
                 return 1;
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index c9e4e5091da1..ce8339c70a4b 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -19,10 +19,18 @@
 #include <linux/poll.h>
 #include <linux/list.h>
 #include <linux/mutex.h>
+#include <linux/limits.h>
 #include <asm/uaccess.h>
 
 #include "sysfs.h"
 
+/* used in crash dumps to help with debugging */
+static char last_sysfs_file[PATH_MAX];
+void sysfs_printk_last_file(void)
+{
+        printk(KERN_EMERG "last sysfs file: %s\n", last_sysfs_file);
+}
+
 /*
  * There's one sysfs_buffer for each open file and one
  * sysfs_open_dirent for each sysfs_dirent with one or more open
@@ -328,6 +336,11 @@ static int sysfs_open_file(struct inode *inode, struct file *file)
         struct sysfs_buffer *buffer;
         struct sysfs_ops *ops;
         int error = -EACCES;
+        char *p;
+
+        p = d_path(&file->f_path, last_sysfs_file, sizeof(last_sysfs_file));
+        if (p)
+                memmove(last_sysfs_file, p, strlen(p) + 1);
 
         /* need attr_sd for attr and ops, its parent for kobj */
         if (!sysfs_get_active_two(attr_sd))
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index 37fa24152bd8..8ec406afb3eb 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -119,6 +119,8 @@ void sysfs_remove_file_from_group(struct kobject *kobj,
 
 void sysfs_notify(struct kobject *kobj, char *dir, char *attr);
 
+void sysfs_printk_last_file(void);
+
 extern int __must_check sysfs_init(void);
 
 #else /* CONFIG_SYSFS */
@@ -231,6 +233,10 @@ static inline int __must_check sysfs_init(void)
         return 0;
 }
 
+static inline void sysfs_printk_last_file(void)
+{
+}
+
 #endif /* CONFIG_SYSFS */
 
 #endif /* _SYSFS_H_ */