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    Subject[PATCH 02/46] sysfs: crash debugging
    Date
    From: Andrew Morton <akpm@linux-foundation.org>

    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>
    ---
    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)
    + 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 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


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