Because liveupdate file handlers will no longer hold a
module reference when registered, we must ensure that the access to
the handler list is protected against concurrent module unloading.
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
kernel/liveupdate/luo_file.c | 61 +++++++++++++++++++++---------------
1 file changed, 35 insertions(+), 26 deletions(-)
diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index 5acee4174bf0..6a0ae29c6a24 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -112,6 +112,7 @@
#include <linux/string.h>
#include "luo_internal.h"
+static DECLARE_RWSEM(luo_file_handler_lock);
static LIST_HEAD(luo_file_handler_list);
/* 2 4K pages, give space for 128 files per file_set */
@@ -277,10 +278,12 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
goto err_fput;
err = -ENOENT;
- list_private_for_each_entry(fh, &luo_file_handler_list, list) {
- if (fh->ops->can_preserve(fh, file)) {
- err = 0;
- break;
+ scoped_guard(rwsem_read, &luo_file_handler_lock) {
+ list_private_for_each_entry(fh, &luo_file_handler_list, list) {
+ if (fh->ops->can_preserve(fh, file)) {
+ err = 0;
+ break;
+ }
}
}
@@ -777,10 +780,12 @@ int luo_file_deserialize(struct luo_file_set *file_set,
bool handler_found = false;
struct luo_file *luo_file;
- list_private_for_each_entry(fh, &luo_file_handler_list, list) {
- if (!strcmp(fh->compatible, file_ser[i].compatible)) {
- handler_found = true;
- break;
+ scoped_guard(rwsem_read, &luo_file_handler_lock) {
+ list_private_for_each_entry(fh, &luo_file_handler_list, list) {
+ if (!strcmp(fh->compatible, file_ser[i].compatible)) {
+ handler_found = true;
+ break;
+ }
}
}
@@ -850,25 +855,27 @@ int liveupdate_register_file_handler(struct liveupdate_file_handler *fh)
if (!luo_session_quiesce())
return -EBUSY;
- /* Check for duplicate compatible strings */
- list_private_for_each_entry(fh_iter, &luo_file_handler_list, list) {
- if (!strcmp(fh_iter->compatible, fh->compatible)) {
- pr_err("File handler registration failed: Compatible string '%s' already registered.\n",
- fh->compatible);
- err = -EEXIST;
+ scoped_guard(rwsem_write, &luo_file_handler_lock) {
+ /* Check for duplicate compatible strings */
+ list_private_for_each_entry(fh_iter, &luo_file_handler_list, list) {
+ if (!strcmp(fh_iter->compatible, fh->compatible)) {
+ pr_err("File handler registration failed: Compatible string '%s' already registered.\n",
+ fh->compatible);
+ err = -EEXIST;
+ goto err_resume;
+ }
+ }
+
+ /* Pin the module implementing the handler */
+ if (!try_module_get(fh->ops->owner)) {
+ err = -EAGAIN;
goto err_resume;
}
- }
- /* Pin the module implementing the handler */
- if (!try_module_get(fh->ops->owner)) {
- err = -EAGAIN;
- goto err_resume;
+ INIT_LIST_HEAD(&ACCESS_PRIVATE(fh, flb_list));
+ INIT_LIST_HEAD(&ACCESS_PRIVATE(fh, list));
+ list_add_tail(&ACCESS_PRIVATE(fh, list), &luo_file_handler_list);
}
-
- INIT_LIST_HEAD(&ACCESS_PRIVATE(fh, flb_list));
- INIT_LIST_HEAD(&ACCESS_PRIVATE(fh, list));
- list_add_tail(&ACCESS_PRIVATE(fh, list), &luo_file_handler_list);
luo_session_resume();
liveupdate_test_register(fh);
@@ -909,10 +916,12 @@ int liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
if (!luo_session_quiesce())
goto err_register;
- if (!list_empty(&ACCESS_PRIVATE(fh, flb_list)))
- goto err_resume;
+ scoped_guard(rwsem_write, &luo_file_handler_lock) {
+ if (!list_empty(&ACCESS_PRIVATE(fh, flb_list)))
+ goto err_resume;
- list_del(&ACCESS_PRIVATE(fh, list));
+ list_del(&ACCESS_PRIVATE(fh, list));
+ }
module_put(fh->ops->owner);
luo_session_resume();
--
2.53.0.851.ga537e3e6e9-googHi Pasha,
On Wed, Mar 18, 2026 at 10:16:39AM -0400, Pasha Tatashin wrote:
> Because liveupdate file handlers will no longer hold a
> module reference when registered, we must ensure that the access to
> the handler list is protected against concurrent module unloading.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
> kernel/liveupdate/luo_file.c | 61 +++++++++++++++++++++---------------
> 1 file changed, 35 insertions(+), 26 deletions(-)
>
> diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
> index 5acee4174bf0..6a0ae29c6a24 100644
> --- a/kernel/liveupdate/luo_file.c
> +++ b/kernel/liveupdate/luo_file.c
> @@ -112,6 +112,7 @@
> #include <linux/string.h>
> #include "luo_internal.h"
>
> +static DECLARE_RWSEM(luo_file_handler_lock);
> static LIST_HEAD(luo_file_handler_list);
>
> /* 2 4K pages, give space for 128 files per file_set */
> @@ -277,10 +278,12 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
> goto err_fput;
>
> err = -ENOENT;
> - list_private_for_each_entry(fh, &luo_file_handler_list, list) {
> - if (fh->ops->can_preserve(fh, file)) {
> - err = 0;
> - break;
> + scoped_guard(rwsem_read, &luo_file_handler_lock) {
I'm not sure scoped_guard() here is better that lock before the loop and
unlock after. scoped_guard() would be useful if we were returning from the
guarded scope.
> + list_private_for_each_entry(fh, &luo_file_handler_list, list) {
> + if (fh->ops->can_preserve(fh, file)) {
> + err = 0;
> + break;
> + }
> }
> }
>
> @@ -777,10 +780,12 @@ int luo_file_deserialize(struct luo_file_set *file_set,
> bool handler_found = false;
> struct luo_file *luo_file;
>
> - list_private_for_each_entry(fh, &luo_file_handler_list, list) {
> - if (!strcmp(fh->compatible, file_ser[i].compatible)) {
> - handler_found = true;
> - break;
> + scoped_guard(rwsem_read, &luo_file_handler_lock) {
> + list_private_for_each_entry(fh, &luo_file_handler_list, list) {
> + if (!strcmp(fh->compatible, file_ser[i].compatible)) {
> + handler_found = true;
> + break;
> + }
Ditto.
> }
> }
>
> @@ -850,25 +855,27 @@ int liveupdate_register_file_handler(struct liveupdate_file_handler *fh)
> if (!luo_session_quiesce())
> return -EBUSY;
>
> - /* Check for duplicate compatible strings */
> - list_private_for_each_entry(fh_iter, &luo_file_handler_list, list) {
> - if (!strcmp(fh_iter->compatible, fh->compatible)) {
> - pr_err("File handler registration failed: Compatible string '%s' already registered.\n",
> - fh->compatible);
> - err = -EEXIST;
> + scoped_guard(rwsem_write, &luo_file_handler_lock) {
> + /* Check for duplicate compatible strings */
> + list_private_for_each_entry(fh_iter, &luo_file_handler_list, list) {
> + if (!strcmp(fh_iter->compatible, fh->compatible)) {
> + pr_err("File handler registration failed: Compatible string '%s' already registered.\n",
> + fh->compatible);
> + err = -EEXIST;
> + goto err_resume;
PeterZ advised against mixing guards() with goto, but unfortunately I can't
find lore link right now.
> + }
> + }
> +
--
Sincerely yours,
Mike.
On Sun, Mar 22, 2026 at 9:13 AM Mike Rapoport <rppt@kernel.org> wrote:
>
> Hi Pasha,
>
> On Wed, Mar 18, 2026 at 10:16:39AM -0400, Pasha Tatashin wrote:
> > Because liveupdate file handlers will no longer hold a
> > module reference when registered, we must ensure that the access to
> > the handler list is protected against concurrent module unloading.
> >
> > Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> > ---
> > kernel/liveupdate/luo_file.c | 61 +++++++++++++++++++++---------------
> > 1 file changed, 35 insertions(+), 26 deletions(-)
> >
> > diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
> > index 5acee4174bf0..6a0ae29c6a24 100644
> > --- a/kernel/liveupdate/luo_file.c
> > +++ b/kernel/liveupdate/luo_file.c
> > @@ -112,6 +112,7 @@
> > #include <linux/string.h>
> > #include "luo_internal.h"
> >
> > +static DECLARE_RWSEM(luo_file_handler_lock);
> > static LIST_HEAD(luo_file_handler_list);
> >
> > /* 2 4K pages, give space for 128 files per file_set */
> > @@ -277,10 +278,12 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
> > goto err_fput;
> >
> > err = -ENOENT;
> > - list_private_for_each_entry(fh, &luo_file_handler_list, list) {
> > - if (fh->ops->can_preserve(fh, file)) {
> > - err = 0;
> > - break;
> > + scoped_guard(rwsem_read, &luo_file_handler_lock) {
>
> I'm not sure scoped_guard() here is better that lock before the loop and
> unlock after. scoped_guard() would be useful if we were returning from the
> guarded scope.
>
> > + list_private_for_each_entry(fh, &luo_file_handler_list, list) {
> > + if (fh->ops->can_preserve(fh, file)) {
> > + err = 0;
> > + break;
> > + }
> > }
> > }
> >
> > @@ -777,10 +780,12 @@ int luo_file_deserialize(struct luo_file_set *file_set,
> > bool handler_found = false;
> > struct luo_file *luo_file;
> >
> > - list_private_for_each_entry(fh, &luo_file_handler_list, list) {
> > - if (!strcmp(fh->compatible, file_ser[i].compatible)) {
> > - handler_found = true;
> > - break;
> > + scoped_guard(rwsem_read, &luo_file_handler_lock) {
> > + list_private_for_each_entry(fh, &luo_file_handler_list, list) {
> > + if (!strcmp(fh->compatible, file_ser[i].compatible)) {
> > + handler_found = true;
> > + break;
> > + }
>
> Ditto.
>
> > }
> > }
> >
> > @@ -850,25 +855,27 @@ int liveupdate_register_file_handler(struct liveupdate_file_handler *fh)
> > if (!luo_session_quiesce())
> > return -EBUSY;
> >
> > - /* Check for duplicate compatible strings */
> > - list_private_for_each_entry(fh_iter, &luo_file_handler_list, list) {
> > - if (!strcmp(fh_iter->compatible, fh->compatible)) {
> > - pr_err("File handler registration failed: Compatible string '%s' already registered.\n",
> > - fh->compatible);
> > - err = -EEXIST;
> > + scoped_guard(rwsem_write, &luo_file_handler_lock) {
> > + /* Check for duplicate compatible strings */
> > + list_private_for_each_entry(fh_iter, &luo_file_handler_list, list) {
> > + if (!strcmp(fh_iter->compatible, fh->compatible)) {
> > + pr_err("File handler registration failed: Compatible string '%s' already registered.\n",
> > + fh->compatible);
> > + err = -EEXIST;
> > + goto err_resume;
>
> PeterZ advised against mixing guards() with goto, but unfortunately I can't
> find lore link right now.
Yeah, I was looking into this yesterday:
https://lore.kernel.org/all/CA+CK2bD2aNu-NByET4KkBP0n2j8WQE2zjxb4g-1cv2hYfjaRZQ@mail.gmail.com
Also, please wait for the next version before reviewing it. I am going
to use what Sami suggested:
https://lore.kernel.org/all/CA+CK2bDONAnry0n9qOsR7GSDTw4Xw3g4ZugRPwXD+NdMx7rpsQ@mail.gmail.com
Pasha
>
> > + }
> > + }
> > +
>
> --
> Sincerely yours,
> Mike.
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