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Tracing and eventfs fixes for 6.8:

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- Fix histogram tracing_map insertion.
   The tracing_map_insert copies the value into the elt variable and
   then assigns the elt to the entry value. But it is possible that
   the entry value becomes visible on other CPUs before the elt is
   fully initialized. This is fixed by adding a wmb() between the
   initialization of the elt variable and assigning it.
 
 - Have eventfs directory have unique inode numbers. Having them be
   all the same proved to be a failure as the find application will
   think that the directories are causing loops, as it checks for
   directory loops via their inodes. Have the evenfs dir entries
   get their inodes assigned when they are referenced and then save
   them in the eventfs_inode structure.
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Merge tag 'trace-v6.8-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull tracing and eventfs fixes from Steven Rostedt:

 - Fix histogram tracing_map insertion.

   The tracing_map_insert copies the value into the elt variable and
   then assigns the elt to the entry value. But it is possible that the
   entry value becomes visible on other CPUs before the elt is fully
   initialized. This is fixed by adding a wmb() between the
   initialization of the elt variable and assigning it.

 - Have eventfs directory have unique inode numbers.

   Having them be all the same proved to be a failure as the 'find'
   application will think that the directories are causing loops, as it
   checks for directory loops via their inodes. Have the evenfs dir
   entries get their inodes assigned when they are referenced and then
   save them in the eventfs_inode structure.

* tag 'trace-v6.8-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  eventfs: Save directory inodes in the eventfs_inode structure
  tracing: Ensure visibility when inserting an element into tracing_map
This commit is contained in:
Linus Torvalds 2024-01-23 16:48:09 -08:00
commit 615d300648
3 changed files with 21 additions and 7 deletions
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14
fs/tracefs/event_inode.c
View File

@ -34,7 +34,15 @@ static DEFINE_MUTEX(eventfs_mutex);
/* Choose something "unique" ;-) */
#define EVENTFS_FILE_INODE_INO 0x12c4e37
#define EVENTFS_DIR_INODE_INO 0x134b2f5
/* Just try to make something consistent and unique */
static int eventfs_dir_ino(struct eventfs_inode *ei)
{
if (!ei->ino)
ei->ino = get_next_ino();
return ei->ino;
}
/*
* The eventfs_inode (ei) itself is protected by SRCU. It is released from
@ -396,7 +404,7 @@ static struct dentry *create_dir(struct eventfs_inode *ei, struct dentry *parent
inode->i_fop = &eventfs_file_operations;
/* All directories will have the same inode number */
inode->i_ino = EVENTFS_DIR_INODE_INO;
inode->i_ino = eventfs_dir_ino(ei);
ti = get_tracefs(inode);
ti->flags |= TRACEFS_EVENT_INODE;
@ -802,7 +810,7 @@ static int eventfs_iterate(struct file *file, struct dir_context *ctx)
name = ei_child->name;
ino = EVENTFS_DIR_INODE_INO;
ino = eventfs_dir_ino(ei_child);
if (!dir_emit(ctx, name, strlen(name), ino, DT_DIR))
goto out_dec;

7
fs/tracefs/internal.h
View File

@ -55,6 +55,10 @@ struct eventfs_inode {
struct eventfs_attr *entry_attrs;
struct eventfs_attr attr;
void *data;
unsigned int is_freed:1;
unsigned int is_events:1;
unsigned int nr_entries:30;
unsigned int ino;
/*
* Union - used for deletion
* @llist: for calling dput() if needed after RCU
@ -64,9 +68,6 @@ struct eventfs_inode {
struct llist_node llist;
struct rcu_head rcu;
};
unsigned int is_freed:1;
unsigned int is_events:1;
unsigned int nr_entries:30;
};
static inline struct tracefs_inode *get_tracefs(const struct inode *inode)

7
kernel/trace/tracing_map.c
View File

@ -574,7 +574,12 @@ __tracing_map_insert(struct tracing_map *map, void *key, bool lookup_only)
}
memcpy(elt->key, key, map->key_size);
entry->val = elt;
/*
* Ensure the initialization is visible and
* publish the elt.
*/
smp_wmb();
WRITE_ONCE(entry->val, elt);
atomic64_inc(&map->hits);
return entry->val;