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    SubjectRe: [RFC v8][PATCH 05/12] x86 support for checkpoint/restart
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    Hi Oren,

    I'm now trying to port your patchset to x86_64, and find a tiny
    inconsistency issue.


    On 2008-10-30 at 09:51 -0400, Oren Laadan wrote:
    > +/* dump the thread_struct of a given task */
    > +int cr_write_thread(struct cr_ctx *ctx, struct task_struct *t)
    > +{
    > + struct cr_hdr h;
    > + struct cr_hdr_thread *hh = cr_hbuf_get(ctx, sizeof(*hh));
    > + struct thread_struct *thread;
    > + struct desc_struct *desc;
    > + int ntls = 0;
    > + int n, ret;
    > +
    > + h.type = CR_HDR_THREAD;
    > + h.len = sizeof(*hh);
    > + h.parent = task_pid_vnr(t);
    > +
    > + thread = &t->thread;
    > +
    > + /* calculate no. of TLS entries that follow */
    > + desc = thread->tls_array;
    > + for (n = GDT_ENTRY_TLS_ENTRIES; n > 0; n--, desc++) {
    > + if (desc->a || desc->b)
    > + ntls++;
    > + }
    > +
    > + hh->gdt_entry_tls_entries = GDT_ENTRY_TLS_ENTRIES;
    > + hh->sizeof_tls_array = sizeof(thread->tls_array);
    > + hh->ntls = ntls;
    > +
    > + ret = cr_write_obj(ctx, &h, hh);
    > + cr_hbuf_put(ctx, sizeof(*hh));
    > + if (ret < 0)
    > + return ret;

    Please add
    if (ntls == 0)
    return ret;
    because, in restart phase, reading TLS entries from the image file
    is skipped if hh->ntls == 0, which may incur inconsistency and fail
    to restart.

    > + /* for simplicity dump the entire array, cherry-pick upon restart */
    > + ret = cr_kwrite(ctx, thread->tls_array, sizeof(thread->tls_array));
    > +
    > + cr_debug("ntls %d\n", ntls);
    > +
    > + /* IGNORE RESTART BLOCKS FOR NOW ... */
    > +
    > + return ret;
    > +}
    (snip)
    > +/* read the thread_struct into the current task */
    > +int cr_read_thread(struct cr_ctx *ctx)
    > +{
    > + struct cr_hdr_thread *hh = cr_hbuf_get(ctx, sizeof(*hh));
    > + struct task_struct *t = current;
    > + struct thread_struct *thread = &t->thread;
    > + int parent, ret;
    > +
    > + parent = cr_read_obj_type(ctx, hh, sizeof(*hh), CR_HDR_THREAD);
    > + if (parent < 0) {
    > + ret = parent;
    > + goto out;
    > + }
    > +
    > + ret = -EINVAL;
    > +
    > +#if 0 /* activate when containers are used */
    > + if (parent != task_pid_vnr(t))
    > + goto out;
    > +#endif
    > + cr_debug("ntls %d\n", hh->ntls);
    > +
    > + if (hh->gdt_entry_tls_entries != GDT_ENTRY_TLS_ENTRIES ||
    > + hh->sizeof_tls_array != sizeof(thread->tls_array) ||
    > + hh->ntls < 0 || hh->ntls > GDT_ENTRY_TLS_ENTRIES)
    > + goto out;
    > +
    > + if (hh->ntls > 0) {
    > + struct desc_struct *desc;
    > + int size, cpu;
    > +
    > + /*
    > + * restore TLS by hand: why convert to struct user_desc if
    > + * sys_set_thread_entry() will convert it back ?
    > + */
    > +
    > + size = sizeof(*desc) * GDT_ENTRY_TLS_ENTRIES;
    > + desc = kmalloc(size, GFP_KERNEL);
    > + if (!desc)
    > + return -ENOMEM;
    > +
    > + ret = cr_kread(ctx, desc, size);
    > + if (ret >= 0) {
    > + /*
    > + * FIX: add sanity checks (eg. that values makes
    > + * sense, that we don't overwrite old values, etc
    > + */
    > + cpu = get_cpu();
    > + memcpy(thread->tls_array, desc, size);
    > + load_TLS(thread, cpu);
    > + put_cpu();
    > + }
    > + kfree(desc);
    > + }
    > +
    > + ret = 0;
    > + out:
    > + cr_hbuf_put(ctx, sizeof(*hh));
    > + return ret;
    > +}


    Thanks,

    Masahiko.

    ---
    Masahiko Takahashi / m-takahashi@ex.jp.nec.com



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