Quoting Matt Helsley ([email protected]):
> Save/restore epoll items during checkpoint/restart respectively.
>
> Tests for the cr_tests suite to follow. Tests pass on i386.
>
> TODOs (search the patch for "TODO") that could probably use some
> comments:
>
> What to do when there's a "possible checkpoint obj leak"? (search patch
> for this string to see what I'm talking about)
>
> Ensure get_current_user will be correct (a userns question/issue?).
>
> kmalloc failures should be dealt with more kindly than just error-out
> because epoll is made to poll many thousands of file
> descriptors.
> This seems like a more general problem with some of the
> ckpt_hdr* functions than an epoll problem but...
>
> Pick better errnos for some cases.
>
> Signed-off-by: Matt Helsley <[email protected]>
> Cc: Oren Laadan <[email protected]>
> ---
> checkpoint/files.c | 35 +++++
> checkpoint/restart.c | 2 +-
> fs/eventpoll.c | 280
> +++++++++++++++++++++++++++++++++++++-
> include/linux/checkpoint.h | 1 +
> include/linux/checkpoint_hdr.h | 14 ++
> include/linux/checkpoint_types.h | 2 +
> include/linux/eventpoll.h | 14 ++-
> 7 files changed, 345 insertions(+), 3 deletions(-)
>
> diff --git a/checkpoint/files.c b/checkpoint/files.c
> index 204055b..8f86dcc 100644
> --- a/checkpoint/files.c
> +++ b/checkpoint/files.c
> @@ -21,6 +21,8 @@
> #include <linux/syscalls.h>
> #include <linux/checkpoint.h>
> #include <linux/checkpoint_hdr.h>
> +#include <linux/deferqueue.h>
> +#include <linux/eventpoll.h>
> #include <net/sock.h>
>
>
> @@ -289,11 +291,24 @@ static int do_checkpoint_file_table(struct ckpt_ctx
> *ctx,
> goto out;
>
> ckpt_debug("nfds %d\n", nfds);
> + ctx->files_deferq = deferqueue_create();
> + if (!ctx->files_deferq) {
> + ret = -ENOMEM;
> + goto out;
> + }
> for (n = 0; n < nfds; n++) {
> ret = checkpoint_file_desc(ctx, files, fdtable[n]);
> if (ret < 0)
> break;
> }
> + if (!ret) {
> + ret = deferqueue_run(ctx->files_deferq);
> + if (ret > 0) {
> + pr_warning("c/r: files deferqueue had %d entries\n",
> ret);
> + ret = 0;
> + }
> + }
> + deferqueue_destroy(ctx->files_deferq);
> out:
> kfree(fdtable);
> return ret;
> @@ -572,6 +587,14 @@ static struct restore_file_ops restore_file_ops[] = {
> .file_type = CKPT_FILE_SOCKET,
> .restore = sock_file_restore,
> },
> +#ifdef CONFIG_EPOLL
> + /* epoll */
> + {
> + .file_name = "EPOLL",
> + .file_type = CKPT_FILE_EPOLL,
> + .restore = ep_file_restore,
> + },
> +#endif
> };
>
> static struct file *do_restore_file(struct ckpt_ctx *ctx)
> @@ -692,11 +715,23 @@ static struct files_struct
> *do_restore_file_table(struct ckpt_ctx *ctx)
> if (ret < 0)
> goto out;
>
> + ret = -ENOMEM;
> + ctx->files_deferq = deferqueue_create();
> + if (!ctx->files_deferq)
> + goto out;
> for (i = 0; i < h->fdt_nfds; i++) {
> ret = restore_file_desc(ctx);
> if (ret < 0)
> break;
> }
> + if (!ret) {
> + ret = deferqueue_run(ctx->files_deferq);
> + if (ret > 0) {
> + pr_warning("c/r: files deferqueue had %d entries\n",
> ret);
> + ret = 0;
> + }
> + }
> + deferqueue_destroy(ctx->files_deferq);
> out:
> ckpt_hdr_put(ctx, h);
> if (!ret) {
> diff --git a/checkpoint/restart.c b/checkpoint/restart.c
> index 4fdae78..3a7d914 100644
> --- a/checkpoint/restart.c
> +++ b/checkpoint/restart.c
> @@ -164,7 +164,7 @@ int _ckpt_read_string(struct ckpt_ctx *ctx, void *ptr,
> int len)
> *
> * Return: new buffer allocated on success, error pointer otherwise
> */
> -static void *ckpt_read_obj(struct ckpt_ctx *ctx, int len, int max)
> +void *ckpt_read_obj(struct ckpt_ctx *ctx, int len, int max)
> {
> struct ckpt_hdr hh;
> struct ckpt_hdr *h;
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index 085c5c0..7f7070f 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -671,10 +671,19 @@ static unsigned int ep_eventpoll_poll(struct file
> *file, poll_table *wait)
> return pollflags != -1 ? pollflags : 0;
> }
>
> +#ifdef CONFIG_CHECKPOINT
> +static int ep_eventpoll_checkpoint(struct ckpt_ctx *ctx, struct file *file);
> +static int ep_file_collect(struct ckpt_ctx *ctx, struct file *file);
> +#else
> +#define ep_eventpoll_checkpoint NULL
Don't forget ep_file_collect here.
> +#endif
> +
> /* File callbacks that implement the eventpoll file behaviour */
> static const struct file_operations eventpoll_fops = {
> .release = ep_eventpoll_release,
> - .poll = ep_eventpoll_poll
> + .poll = ep_eventpoll_poll,
> + .checkpoint = ep_eventpoll_checkpoint,
> + .collect = ep_file_collect,
> };
>
> /* Fast test to see if the file is an evenpoll file */
> @@ -1413,6 +1422,275 @@ SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct
> epoll_event __user *, events,
>
> #endif /* HAVE_SET_RESTORE_SIGMASK */
>
> +#ifdef CONFIG_CHECKPOINT
> +#include <linux/checkpoint.h>
> +#include <linux/checkpoint_hdr.h>
> +#include <linux/deferqueue.h>
> +
> +static int ep_file_collect(struct ckpt_ctx *ctx, struct file *file)
> +{
> + struct rb_node *rbp;
> + struct eventpoll *ep;
> + int ret = 0;
> +
> + if (!is_file_epoll(file))
> + return 0;
> +
> + ep = file->private_data;
> + mutex_lock(&ep->mtx);
> + for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
> + struct epitem *epi;
> +
> + epi = rb_entry(rbp, struct epitem, rbn);
> + ret = ckpt_obj_collect(ctx, epi->ffd.file, CKPT_OBJ_FILE);
> + if (ret < 0)
> + break;
> + }
> + mutex_unlock(&ep->mtx);
> + return ret;
> +}
> +
> +struct epoll_deferq_entry {
> + struct ckpt_ctx *ctx;
> + struct file *epfile;
> +};
> +
> +static int ep_items_checkpoint(void *data)
> +{
> + struct epoll_deferq_entry *ep_dq_entry = data;
> + struct ckpt_ctx *ctx;
> + struct file *file;
> + struct ckpt_eventpoll_items *h;
> + struct rb_node *rbp;
> + struct eventpoll *ep;
> + int i, ret = -ENOMEM;
> +
> + file = ep_dq_entry->epfile;
> + ctx = ep_dq_entry->ctx;
> +
> + ep = file->private_data;
> + mutex_lock(&ep->mtx);
> + for (i = 0, rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp), i++) {}
> + mutex_unlock(&ep->mtx);
> +
> + /* TODO likely allocation failure when lots of epoll items */
> + h = ckpt_hdr_get_type(ctx, sizeof(*h) + i*sizeof(h->items[0]),
> + CKPT_HDR_FILE_EPOLL_ITEMS);
> + if (!h)
> + goto out;
> +
> + ret = -ENODEV;
> + h->num_items = i;
> + h->epfile_objref = ckpt_obj_lookup(ctx, file, CKPT_OBJ_FILE);
> + if (h->epfile_objref <= 0)
> + goto out;
> +
> + ret = 0;
> + mutex_lock(&ep->mtx);
> + for (i = 0, rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp), i++) {
> + struct epitem *epi;
> + int objref;
> +
> + epi = rb_entry(rbp, struct epitem, rbn);
> + objref = ckpt_obj_lookup(ctx, epi->ffd.file, CKPT_OBJ_FILE);
> + if (objref <= 0) {
> + /* TODO error -- possible checkpoint obj leak */
> + ret = -ENODEV;
> + break;
> + }
> + h->items[i].fd = epi->ffd.fd;
> + h->items[i].file_objref = objref;
> + h->items[i].events = epi->event.events;
> + h->items[i].data = epi->event.data;
> + }
> + mutex_unlock(&ep->mtx);
> + if (h && !ret)
> + ret = ckpt_write_obj(ctx, &h->h);
> + if (!ret && (i != h->num_items)) {
> + /* TODO error -- possible checkpoint obj leak */
> + }
> +out:
> + if (h)
> + ckpt_hdr_put(ctx, &h->h);
> + return ret;
> +}
> +
> +static int ep_eventpoll_checkpoint(struct ckpt_ctx *ctx, struct file *file)
> +{
> + struct ckpt_hdr_file *h;
> + struct epoll_deferq_entry ep_dq_entry;
> + int ret = -ENOMEM;
> +
> + h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_FILE);
> + if (!h)
> + goto out_print;
> + h->f_type = CKPT_FILE_EPOLL;
> + ret = checkpoint_file_common(ctx, file, h);
> + if (ret < 0)
> + goto out;
> + ret = ckpt_write_obj(ctx, &h->h);
> + if (ret < 0)
> + goto out;
> +
> + /*
> + * Defer saving the epoll items until all of the ffd.file pointers
> + * have an objref; after the file table has been checkpointed.
> + */
> + ep_dq_entry.ctx = ctx;
> + ep_dq_entry.epfile = file;
> + ret = deferqueue_add(ctx->files_deferq, &ep_dq_entry,
> + sizeof(ep_dq_entry), ep_items_checkpoint, NULL);
> +out:
> + ckpt_hdr_put(ctx, h);
> +out_print:
> + return ret;
> +}
> +
> +static int ep_items_restore(void *data)
> +{
> + struct ckpt_ctx *ctx = *((struct ckpt_ctx**)data);
> + struct ckpt_eventpoll_items *h;
> + struct eventpoll *ep;
> + struct file *epfile = NULL;
> + int ret, i = 0, remaining_watches;
> +
> + /*
> + * TODO possible kmalloc failure due to too many watches.
> + */
> + h = ckpt_read_obj(ctx, 0,
> + sizeof(*h) + max_user_watches*sizeof(h->items[0]));
> + if (IS_ERR(h))
> + return PTR_ERR(h);
> +
> + ret = -EINVAL;
> + if ((h->h.type != CKPT_HDR_FILE_EPOLL_ITEMS) ||
> + (h->h.len < sizeof(*h)))
> + goto out;
> +
> + /* Make sure the items match the size we expect */
> + if (h->num_items != ((h->h.len - sizeof(*h)) / sizeof(h->items[0])))
> + goto out;
> +
> + epfile = ckpt_obj_fetch(ctx, h->epfile_objref, CKPT_OBJ_FILE);
> + if (IS_ERR(epfile)) {
> + ret = PTR_ERR(epfile);
> + goto out;
> + }
> + ret = -ENOMSG;
> + if (!is_file_epoll(epfile))
> + goto out;
> +
> + ep = epfile->private_data;
> +
> + ret = -ENOSPC;
> + remaining_watches = (max_user_watches -
> + atomic_read(&ep->user->epoll_watches));
> + if (h->num_items > remaining_watches)
> + goto out;
> +
> + ret = 0;
> + /* Restore the epoll items/watches */
> + for (i = 0; !ret && i < h->num_items; i++) {
> + /*
> + * Loop body like multiple epoll_ctl(ep, ADD, event)
> + * calls except we've already done much of the checking.
> + */
> + struct epoll_event epev;
> + struct epitem *epi;
> + struct file *tfile;
> +
> + epev.events = h->items[i].events;
> + epev.data = h->items[i].data;
> +
> + /* Get the file* for the target file */
> + if (h->items[i].file_objref <= 0) {
> + ret = -EINVAL;
> + break;
> + }
> +
> + tfile = ckpt_obj_fetch(ctx, h->items[i].file_objref,
> + CKPT_OBJ_FILE);
> + if (IS_ERR(tfile)) {
> + ret = PTR_ERR(tfile);
> + break;
> + }
> +
> + /* The target file must support poll */
> + if (!tfile->f_op || !tfile->f_op->poll) {
> + ret = -EPERM;
> + break;
> + }
> +
> + /* Cannot add an epoll file descriptor inside itself. */
> + if (epfile == tfile) {
> + ret = -EINVAL;
> + break;
> + }
> +
> + mutex_lock(&ep->mtx);
> + epi = ep_find(ep, tfile, h->items[i].fd);
> + if (!epi) {
> + epev.events |= POLLERR | POLLHUP;
> + ret = ep_insert(ep, &epev, tfile, h->items[i].fd);
> + } else
> + ret = -EEXIST;
> + mutex_unlock(&ep->mtx);
> + }
> +out:
> + ckpt_hdr_put(ctx, h);
> + return ret;
> +}
> +
> +/* TODO confirm that get_current_user() has been restored */
Not sure what you mean. At this point, the task's credentials
are still the ones used when it called sys_restart(). We won't
update them until the end of the restart operation. However the
normal file restore operations should have reset the file->f_cred
to the checkpointed value - including hierarchical user namespaces.
> +struct file* ep_file_restore(struct ckpt_ctx *ctx,
> + struct ckpt_hdr_file *h)
> +{
> + struct file *epfile;
> + int epfd, ret;
> +
> + if (h->h.type != CKPT_HDR_FILE ||
> + h->h.len != sizeof(*h) ||
> + h->f_type != CKPT_FILE_EPOLL)
> + return ERR_PTR(-EINVAL);
> +
> + /*
> + * TODO Normally h->f_flags contains flags that epoll_create() won't
> + * accept. Right now we pass only those flags it will accept here
> + * and restore the rest during the "common" file restore. Check
> + * to make sure we're not missing anything.
> + */
> + epfd = sys_epoll_create1(h->f_flags & EPOLL_CLOEXEC);
> + if (epfd < 0)
> + return ERR_PTR(epfd);
> + epfile = fget(epfd);
> + if (!epfile)
> + return ERR_PTR(-ENOENT); /* TODO pick better error? */
> +
> + ret = restore_file_common(ctx, epfile, h);
> + if (ret < 0)
> + goto fput_out;
> +
> + /*
> + * Now we have the file and file descriptor but the epoll set is empty.
> + * Defer restoring the epoll set until we encounter its corresponding
> + * items. Note that this effectively counts the number of
> + * ckpt_eventpoll_items blocks we should expect -- we rely on the
> + * epfile_objref of those blocks to associate them with the proper
> + * file.
> + */
> + ret = deferqueue_add(ctx->files_deferq, &ctx, sizeof(ctx),
> + ep_items_restore, NULL);
> + if (ret < 0) {
> +fput_out:
> + fput(epfile);
> + epfile = ERR_PTR(ret);
> + }
> + sys_close(epfd);
> + return epfile;
> +}
> +
> +#endif /* CONFIG_CHECKPOINT */
> +
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