Re: [PATCH 02/46] sysfs: crash debugging

From: Mathieu Desnoyers
Date: Thu Oct 16 2008 - 13:41:37 EST


* Greg Kroah-Hartman (gregkh@xxxxxxx) wrote:
> From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>
> 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@xxxxxxxx>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
> ---
> arch/x86/kernel/dumpstack_32.c | 2 ++
> arch/x86/kernel/dumpstack_64.c | 2 ++
> fs/sysfs/file.c | 13 +++++++++++++
> include/linux/sysfs.h | 6 ++++++
> 4 files changed, 23 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/kernel/dumpstack_32.c b/arch/x86/kernel/dumpstack_32.c
> index 201ee35..1a78180 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 086cc81..96a5db7 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 c9e4e50..ce8339c 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)

if (!IS_ERR(p)) ?

> + memmove(last_sysfs_file, p, strlen(p) + 1);
>

Given we do a strlen() here anyway, shouldn't we just use strcpy ?

Mathieu

> /* 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 37fa241..8ec406a 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_ */
> --
> 1.6.0.2
>

--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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