[Devel] [PATCH VZ10 v3 3/9] ve/fs: Rework per-ve mount count
Pavel Tikhomirov
ptikhomirov at virtuozzo.com
Fri Jul 31 12:56:18 MSK 2026
On 7/26/26 23:30, Vladimir Riabchun wrote:
> Previous approach with current mounts counter had an issue:
> there was a gap between ve_mount_allowed check and ve_mount_nr_inc,
> which could allow CT to have more mounts than expected.
>
> Fix this by tracking the number of available mounts instead
> of current ones. This also makes resources accounting
> more consistent - we are using ***_avail_nr approach more.
>
> One more issue with inconsistent ve value is fixed:
> ve_mount_allowed always used ve from get_exec_env, but
> ve_mount_nr_inc operated with owner_ve.
> Now actual ve value is calculated in the beginning of alloc_vfsmnt.
>
> We can't ignore pseudouser mode, otherwise CRIU may fail when
> the number of mounts is close to the limit.
> It is possible to create a mount as a pseudouser and then do umount
> as a normal user. To prevent incorrect accounting and treat
> pseudouser mode special, a new field created_as_pseudouser was added
> to mount structure.
>
> https://virtuozzo.atlassian.net/browse/VSTOR-135520
>
> Feature: per-ve failcounters
> Signed-off-by: Vladimir Riabchun <vladimir.riabchun at virtuozzo.com>
> ---
> fs/mount.h | 1 +
> fs/namespace.c | 66 ++++++++++++++++++++++++++--------------------
> include/linux/ve.h | 2 +-
> kernel/ve/ve.c | 12 ++++-----
> 4 files changed, 45 insertions(+), 36 deletions(-)
>
> diff --git a/fs/mount.h b/fs/mount.h
> index 5cf06431d586..2ea5248c64e0 100644
> --- a/fs/mount.h
> +++ b/fs/mount.h
> @@ -72,6 +72,7 @@ struct mount {
> struct list_head mnt_umounting; /* list entry for umount propagation */
> #ifdef CONFIG_VE
> struct ve_struct *ve_owner; /* VE in which this mount was created */
> + bool created_as_pseudouser; /* pseudouser mounts ignore per-VE limits */
> #endif /* CONFIG_VE */
> #ifdef CONFIG_FSNOTIFY
> struct fsnotify_mark_connector __rcu *mnt_fsnotify_marks;
> diff --git a/fs/namespace.c b/fs/namespace.c
> index cd6aa2127203..6811082360cc 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -317,18 +317,21 @@ int mnt_get_count(struct mount *mnt)
> #endif
> }
>
> -static inline int ve_mount_allowed(void);
> -static inline void ve_mount_nr_inc(struct mount *mnt, struct ve_struct *ve);
> -static inline void ve_mount_nr_dec(struct mount *mnt);
> +static inline int ve_try_reserve_mount(struct ve_struct *ve);
> +static inline void ve_mount_put(struct mount *mnt, struct ve_struct *ve);
>
> static struct mount *alloc_vfsmnt(const char *name, struct ve_struct *owner_ve)
> {
> struct mount *mnt;
> + struct ve_struct *ve = owner_ve;
>
> - if (!ve_mount_allowed()) {
> + if (!ve)
> + ve = get_exec_env();
> +
> + if (!ve_try_reserve_mount(ve)) {
> pr_warn_ratelimited(
> "CT#%s reached the limit on mounts.\n",
> - ve_name(get_exec_env()));
> + ve_name(ve));
> return NULL;
> }
>
> @@ -370,7 +373,13 @@ static struct mount *alloc_vfsmnt(const char *name, struct ve_struct *owner_ve)
> INIT_LIST_HEAD(&mnt->mnt_umounting);
> INIT_HLIST_HEAD(&mnt->mnt_stuck_children);
> mnt->mnt.mnt_idmap = &nop_mnt_idmap;
> - ve_mount_nr_inc(mnt, owner_ve);
> +#ifdef CONFIG_VE
> + /* Got ve reference in ve_try_reserve_mount */
> + mnt->ve_owner = ve;
> + mnt->created_as_pseudouser = ve->is_pseudosuper;
> +#endif
> + } else {
> + goto out_nomem;
> }
> return mnt;
>
> @@ -382,6 +391,9 @@ static struct mount *alloc_vfsmnt(const char *name, struct ve_struct *owner_ve)
> mnt_free_id(mnt);
> out_free_cache:
> kmem_cache_free(mnt_cache, mnt);
> +out_nomem:
> + /* Got ve reference in ve_try_reserve_mount */
> + ve_mount_put(mnt, ve);
> return NULL;
> }
>
> @@ -750,7 +762,7 @@ int sb_prepare_remount_readonly(struct super_block *sb)
> static void free_vfsmnt(struct mount *mnt)
> {
> mnt_idmap_put(mnt_idmap(&mnt->mnt));
> - ve_mount_nr_dec(mnt);
> + ve_mount_put(mnt, mnt->ve_owner);
> kfree_const(mnt->mnt_devname);
> #ifdef CONFIG_SMP
> free_percpu(mnt->mnt_pcp);
> @@ -3258,30 +3270,27 @@ int ve_devmnt_process(struct ve_struct *ve, dev_t dev, void **data_pp, int remou
> return err;
> }
>
> -static inline int ve_mount_allowed(void)
> -{
> - struct ve_struct *ve = get_exec_env();
> -
> - return ve_is_super(ve) || ve->is_pseudosuper ||
> - atomic_read(&ve->mnt_nr) < (int)sysctl_ve_mount_nr;
> -}
> -
> -static inline void ve_mount_nr_inc(struct mount *mnt, struct ve_struct *ve)
> +static inline int ve_try_reserve_mount(struct ve_struct *ve)
> {
> - if (!ve)
> - ve = get_exec_env();
> -
> - mnt->ve_owner = get_ve(ve);
> - atomic_inc(&ve->mnt_nr);
> + int ret = ve_is_super(ve) || ve->is_pseudosuper ||
> + atomic_dec_if_positive(&ve->mnt_avail_nr) >= 0;
Nacked-by: Pavel Tikhomirov <ptikhomirov at viruozzo.com>
All this created_as_pseudouser makes no sense. Container after c/r
should have all it's mounts accounted in mnt_avail_nr. Now each time
we c/r we reset the counter to maximum again.
Again, please do as it was before:
1) we ALWAYS update the count when mount is created/removed
2) super and pseudouper ignore the limit so avail counter can get negative
3) regular container user fails to allocate mounts if avail counter is <= 0.
> + if (ret)
> + get_ve(ve);
> + return ret;
> }
>
> -static inline void ve_mount_nr_dec(struct mount *mnt)
> +static inline void ve_mount_put(struct mount *mnt, struct ve_struct *ve)
> {
> - struct ve_struct *ve = mnt->ve_owner;
> -
> - atomic_dec(&ve->mnt_nr);
> + /*
> + * ve argument is needed to reuse this function in alloc_vfsmnt error path.
> + * Other users should pass mnt->ve_owner value.
> + */
> + if (!ve_is_super(ve) && !(mnt && mnt->created_as_pseudouser) &&
> + !(!mnt && ve->is_pseudosuper))
> + atomic_inc(&ve->mnt_avail_nr);
> put_ve(ve);
> - mnt->ve_owner = NULL;
> + if (mnt)
> + mnt->ve_owner = NULL;
> }
>
> bool is_sb_ve_accessible(struct ve_struct *ve, struct super_block *sb)
> @@ -3303,9 +3312,8 @@ bool is_sb_ve_accessible(struct ve_struct *ve, struct super_block *sb)
>
> #else /* CONFIG_VE */
>
> -static inline int ve_mount_allowed(void) { return 1; }
> -static inline void ve_mount_nr_inc(struct mount *mnt, struct ve_struct *ve) { }
> -static inline void ve_mount_nr_dec(struct mount *mnt) { }
> +static inline int ve_try_reserve_mount(struct ve_struct *ve) { return 1; }
> +static inline void ve_mount_put(struct mount *mnt, struct ve_struct *ve) { }
> #endif /* CONFIG_VE */
>
> static int ve_prepare_mount_options(struct fs_context *fc, void *data)
> diff --git a/include/linux/ve.h b/include/linux/ve.h
> index 3facbd1759df..cca0a2bc1aac 100644
> --- a/include/linux/ve.h
> +++ b/include/linux/ve.h
> @@ -88,7 +88,7 @@ struct ve_struct {
> atomic_t nd_neigh_nr;
> unsigned long meminfo_val;
>
> - atomic_t mnt_nr; /* number of present VE mounts */
> + atomic_t mnt_avail_nr; /* number of available VE mounts */
>
> #ifdef CONFIG_COREDUMP
> char core_pattern[CORENAME_MAX_SIZE];
> diff --git a/kernel/ve/ve.c b/kernel/ve/ve.c
> index dddf2393326d..3f66144eeb7e 100644
> --- a/kernel/ve/ve.c
> +++ b/kernel/ve/ve.c
> @@ -81,7 +81,7 @@ struct ve_struct ve0 = {
>
> .arp_neigh_nr = ATOMIC_INIT(0),
> .nd_neigh_nr = ATOMIC_INIT(0),
> - .mnt_nr = ATOMIC_INIT(0),
> + .mnt_avail_nr = ATOMIC_INIT(INT_MAX),
> .meminfo_val = VE_MEMINFO_SYSTEM,
> .umh_running_helpers = ATOMIC_INIT(0),
> .umh_helpers_waitq = __WAIT_QUEUE_HEAD_INITIALIZER(ve0.umh_helpers_waitq),
> @@ -778,7 +778,7 @@ static struct cgroup_subsys_state *ve_create(struct cgroup_subsys_state *parent_
>
> atomic_set(&ve->arp_neigh_nr, 0);
> atomic_set(&ve->nd_neigh_nr, 0);
> - atomic_set(&ve->mnt_nr, 0);
> + atomic_set(&ve->mnt_avail_nr, sysctl_ve_mount_nr);
>
> #ifdef CONFIG_COREDUMP
> strcpy(ve->core_pattern, "core");
> @@ -1055,9 +1055,9 @@ static u64 ve_netns_avail_nr_read(struct cgroup_subsys_state *css, struct cftype
> return atomic_read(&css_to_ve(css)->netns_avail_nr);
> }
>
> -static u64 ve_mnt_nr_read(struct cgroup_subsys_state *css, struct cftype *cft)
> +static s64 ve_mnt_avail_nr_read(struct cgroup_subsys_state *css, struct cftype *cft)
> {
> - return atomic_read(&css_to_ve(css)->mnt_nr);
> + return atomic_read(&css_to_ve(css)->mnt_avail_nr);
> }
>
> static u64 ve_netif_max_nr_read(struct cgroup_subsys_state *css, struct cftype *cft)
> @@ -1617,8 +1617,8 @@ static struct cftype ve_cftypes[] = {
> .read_u64 = ve_netns_avail_nr_read,
> },
> {
> - .name = "mnt_nr",
> - .read_u64 = ve_mnt_nr_read,
> + .name = "mnt_avail_nr",
> + .read_s64 = ve_mnt_avail_nr_read,
> },
> {
> .name = "netif_max_nr",
--
Best regards, Pavel Tikhomirov
Senior Software Developer, Virtuozzo.
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