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    Subject[PATCH v4 20/20] futex: Dump internal futex state via debugfs
    Date
    For debugging purpose, it is sometimes useful to dump the internal
    states in the futex hash bucket table. This patch adds a file
    "futex_hash_table" in debugfs root filesystem to dump the internal
    futex states.

    Signed-off-by: Waiman Long <longman@redhat.com>
    ---
    kernel/futex.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
    1 file changed, 82 insertions(+)

    diff --git a/kernel/futex.c b/kernel/futex.c
    index 4f235e8..9f7bfd3 100644
    --- a/kernel/futex.c
    +++ b/kernel/futex.c
    @@ -4425,3 +4425,85 @@ static int __init futex_init(void)
    return 0;
    }
    __initcall(futex_init);
    +
    +#if defined(CONFIG_DEBUG_FS) && defined(CONFIG_SMP)
    +/*
    + * Debug code to dump selected content of in-kernel futex hash bucket table.
    + */
    +#include <linux/debugfs.h>
    +
    +static int futex_dump_show(struct seq_file *m, void *arg)
    +{
    + struct futex_hash_bucket *hb = arg;
    + struct futex_state *state;
    + int i;
    +
    + if (list_empty(&hb->fs_head))
    + return 0;
    +
    + seq_printf(m, "\nHash bucket %ld:\n", hb - futex_queues);
    + spin_lock(&hb->fs_lock);
    + i = 0;
    + list_for_each_entry(state, &hb->fs_head, fs_list) {
    + seq_printf(m, " Futex state %d\n", i++);
    + if (state->owner)
    + seq_printf(m, " owner PID = %d\n",
    + task_pid_vnr(state->owner));
    + if (state->mutex_owner)
    + seq_printf(m, " mutex owner PID = %d\n",
    + task_pid_vnr(state->mutex_owner));
    + seq_printf(m, " reference count = %d\n",
    + atomic_read(&state->refcount));
    + seq_printf(m, " handoff PID = %d\n", state->handoff_pid);
    + }
    + spin_unlock(&hb->fs_lock);
    + return 0;
    +}
    +
    +static void *futex_dump_start(struct seq_file *m, loff_t *pos)
    +{
    + return (*pos < futex_hashsize) ? &futex_queues[*pos] : NULL;
    +}
    +
    +static void *futex_dump_next(struct seq_file *m, void *arg, loff_t *pos)
    +{
    + (*pos)++;
    + return (*pos < futex_hashsize) ? &futex_queues[*pos] : NULL;
    +}
    +
    +static void futex_dump_stop(struct seq_file *m, void *arg)
    +{
    +}
    +
    +static const struct seq_operations futex_dump_op = {
    + .start = futex_dump_start,
    + .next = futex_dump_next,
    + .stop = futex_dump_stop,
    + .show = futex_dump_show,
    +};
    +
    +static int futex_dump_open(struct inode *inode, struct file *file)
    +{
    + return seq_open(file, &futex_dump_op);
    +}
    +
    +static const struct file_operations fops_futex_dump = {
    + .open = futex_dump_open,
    + .read = seq_read,
    + .llseek = seq_lseek,
    + .release = seq_release,
    +};
    +
    +/*
    + * Initialize debugfs for the futex hash bucket table dump.
    + */
    +static int __init init_futex_dump(void)
    +{
    + if (!debugfs_create_file("futex_hash_table", 0400, NULL, NULL,
    + &fops_futex_dump))
    + return -ENOMEM;
    + return 0;
    +}
    +fs_initcall(init_futex_dump);
    +
    +#endif /* CONFIG_DEBUG_FS && CONFIG_SMP */
    --
    1.8.3.1
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