From: "Steven Rostedt (Google)" rostedt@goodmis.org
The eventfs_inode (ei) is protected by SRCU, but the ei->dentry is not. It is protected by the eventfs_mutex. Anytime the eventfs_mutex is released, and access to the ei->dentry needs to be done, it should first check if ei->is_freed is set under the eventfs_mutex. If it is, then the ei->dentry is invalid and must not be used. The ei->dentry must only be accessed under the eventfs_mutex and after checking if ei->is_freed is set.
When the ei is being freed, it will (under the eventfs_mutex) set is_freed and at the same time move the dentry to a free list to be cleared after the eventfs_mutex is released. This means that any access to the ei->dentry must check first if ei->is_freed is set, because if it is, then the dentry is on its way to be freed.
Also add comments to describe this better.
Link: https://lore.kernel.org/all/CA+G9fYt6pY+tMZEOg=SoEywQOe19fGP3uR15SGowkdK+_X8... Link: https://lore.kernel.org/all/CA+G9fYuDP3hVQ3t7FfrBAjd_WFVSurMgCepTxunSJf=MTe=... Link: https://lkml.kernel.org/r/20231101172649.477608228@goodmis.org
Cc: Ajay Kaher akaher@vmware.com Cc: Mark Rutland mark.rutland@arm.com Cc: Andrew Morton akpm@linux-foundation.org Fixes: 5790b1fb3d672 ("eventfs: Remove eventfs_file and just use eventfs_inode") Reported-by: Linux Kernel Functional Testing lkft@linaro.org Reported-by: Naresh Kamboju naresh.kamboju@linaro.org Reported-by: Beau Belgrave beaub@linux.microsoft.com Reviewed-by: Masami Hiramatsu (Google) mhiramat@kernel.org Tested-by: Linux Kernel Functional Testing lkft@linaro.org Tested-by: Naresh Kamboju naresh.kamboju@linaro.org Tested-by: Beau Belgrave beaub@linux.microsoft.com Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org (cherry picked from commit 77a06c33a22d13f3a6e31f06f6ee6bca666e6898) --- fs/tracefs/event_inode.c | 45 ++++++++++++++++++++++++++++++++++------ fs/tracefs/internal.h | 3 ++- 2 files changed, 41 insertions(+), 7 deletions(-)
diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c index dd5971855732..e9625732c52d 100644 --- a/fs/tracefs/event_inode.c +++ b/fs/tracefs/event_inode.c @@ -24,7 +24,20 @@ #include <linux/delay.h> #include "internal.h"
+/* + * eventfs_mutex protects the eventfs_inode (ei) dentry. Any access + * to the ei->dentry must be done under this mutex and after checking + * if ei->is_freed is not set. The ei->dentry is released under the + * mutex at the same time ei->is_freed is set. If ei->is_freed is set + * then the ei->dentry is invalid. + */ static DEFINE_MUTEX(eventfs_mutex); + +/* + * The eventfs_inode (ei) itself is protected by SRCU. It is released from + * its parent's list and will have is_freed set (under eventfs_mutex). + * After the SRCU grace period is over, the ei may be freed. + */ DEFINE_STATIC_SRCU(eventfs_srcu);
static struct dentry *eventfs_root_lookup(struct inode *dir, @@ -239,6 +252,10 @@ create_file_dentry(struct eventfs_inode *ei, struct dentry **e_dentry, bool invalidate = false;
mutex_lock(&eventfs_mutex); + if (ei->is_freed) { + mutex_unlock(&eventfs_mutex); + return NULL; + } /* If the e_dentry already has a dentry, use it */ if (*e_dentry) { /* lookup does not need to up the ref count */ @@ -312,6 +329,8 @@ static void eventfs_post_create_dir(struct eventfs_inode *ei) struct eventfs_inode *ei_child; struct tracefs_inode *ti;
+ lockdep_assert_held(&eventfs_mutex); + /* srcu lock already held */ /* fill parent-child relation */ list_for_each_entry_srcu(ei_child, &ei->children, list, @@ -325,6 +344,7 @@ static void eventfs_post_create_dir(struct eventfs_inode *ei)
/** * create_dir_dentry - Create a directory dentry for the eventfs_inode + * @pei: The eventfs_inode parent of ei. * @ei: The eventfs_inode to create the directory for * @parent: The dentry of the parent of this directory * @lookup: True if this is called by the lookup code @@ -332,12 +352,17 @@ static void eventfs_post_create_dir(struct eventfs_inode *ei) * This creates and attaches a directory dentry to the eventfs_inode @ei. */ static struct dentry * -create_dir_dentry(struct eventfs_inode *ei, struct dentry *parent, bool lookup) +create_dir_dentry(struct eventfs_inode *pei, struct eventfs_inode *ei, + struct dentry *parent, bool lookup) { bool invalidate = false; struct dentry *dentry = NULL;
mutex_lock(&eventfs_mutex); + if (pei->is_freed || ei->is_freed) { + mutex_unlock(&eventfs_mutex); + return NULL; + } if (ei->dentry) { /* If the dentry already has a dentry, use it */ dentry = ei->dentry; @@ -440,7 +465,7 @@ static struct dentry *eventfs_root_lookup(struct inode *dir, */ mutex_lock(&eventfs_mutex); ei = READ_ONCE(ti->private); - if (ei) + if (ei && !ei->is_freed) ei_dentry = READ_ONCE(ei->dentry); mutex_unlock(&eventfs_mutex);
@@ -454,7 +479,7 @@ static struct dentry *eventfs_root_lookup(struct inode *dir, if (strcmp(ei_child->name, name) != 0) continue; ret = simple_lookup(dir, dentry, flags); - create_dir_dentry(ei_child, ei_dentry, true); + create_dir_dentry(ei, ei_child, ei_dentry, true); created = true; break; } @@ -588,7 +613,7 @@ static int dcache_dir_open_wrapper(struct inode *inode, struct file *file)
list_for_each_entry_srcu(ei_child, &ei->children, list, srcu_read_lock_held(&eventfs_srcu)) { - d = create_dir_dentry(ei_child, parent, false); + d = create_dir_dentry(ei, ei_child, parent, false); if (d) { ret = add_dentries(&dentries, d, cnt); if (ret < 0) @@ -705,12 +730,20 @@ struct eventfs_inode *eventfs_create_dir(const char *name, struct eventfs_inode ei->nr_entries = size; ei->data = data; INIT_LIST_HEAD(&ei->children); + INIT_LIST_HEAD(&ei->list);
mutex_lock(&eventfs_mutex); - list_add_tail(&ei->list, &parent->children); - ei->d_parent = parent->dentry; + if (!parent->is_freed) { + list_add_tail(&ei->list, &parent->children); + ei->d_parent = parent->dentry; + } mutex_unlock(&eventfs_mutex);
+ /* Was the parent freed? */ + if (list_empty(&ei->list)) { + free_ei(ei); + ei = NULL; + } return ei; }
diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h index c7d88aaa949f..5a98e87dd3d1 100644 --- a/fs/tracefs/internal.h +++ b/fs/tracefs/internal.h @@ -24,6 +24,7 @@ struct tracefs_inode { * @d_children: The array of dentries to represent the files when created * @data: The private data to pass to the callbacks * @is_freed: Flag set if the eventfs is on its way to be freed + * Note if is_freed is set, then dentry is corrupted. * @nr_entries: The number of items in @entries */ struct eventfs_inode { @@ -31,7 +32,7 @@ struct eventfs_inode { const struct eventfs_entry *entries; const char *name; struct list_head children; - struct dentry *dentry; + struct dentry *dentry; /* Check is_freed to access */ struct dentry *d_parent; struct dentry **d_children; void *data;