> On 01-Jul-2023, at 7:24 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > !! External Email > > FYI, all subjects should start with a capital letter: > > "eventfs: Implement eventfs dir creation functions" > > On Thu, 1 Jun 2023 14:30:06 +0530 > Ajay Kaher <akaher@xxxxxxxxxx> wrote: > >> Adding eventfs_file structure which will hold properties of file or dir. >> >> Adding following functions to add dir in eventfs: >> >> eventfs_create_events_dir() directly creates events dir with-in > > "within" is a proper word. > >> tracing folder. >> >> eventfs_add_subsystem_dir() adds the information of subsystem_dir to >> eventfs and dynamically creates subsystem_dir as and when requires. > > "as and when requires" does not make sense. > >> >> eventfs_add_dir() adds the information of dir (which is with-in > > "within" > >> subsystem_dir) to eventfs and dynamically creates these dir as >> and when requires. > > I'm guessing you want to say: > > eventfs_add_dir() adds the information of the dir, within a > subsystem_dir, to eventfs and dynamically creates these > directories when they are accessed. > >> >> Signed-off-by: Ajay Kaher <akaher@xxxxxxxxxx> >> Co-developed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> >> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> >> Tested-by: Ching-lin Yu <chinglinyu@xxxxxxxxxx> >> Reported-by: kernel test robot <lkp@xxxxxxxxx> >> Link: https://lore.kernel.org/oe-lkp/202305051619.9a469a9a-yujie.liu@xxxxxxxxx >> --- >> fs/tracefs/Makefile | 1 + >> fs/tracefs/event_inode.c | 272 +++++++++++++++++++++++++++++++++++++++ >> include/linux/tracefs.h | 29 +++++ >> kernel/trace/trace.h | 1 + >> 4 files changed, 303 insertions(+) >> create mode 100644 fs/tracefs/event_inode.c >> >> diff --git a/fs/tracefs/Makefile b/fs/tracefs/Makefile >> index 7c35a282b..73c56da8e 100644 >> --- a/fs/tracefs/Makefile >> +++ b/fs/tracefs/Makefile >> @@ -1,5 +1,6 @@ >> # SPDX-License-Identifier: GPL-2.0-only >> tracefs-objs := inode.o >> +tracefs-objs += event_inode.o >> >> obj-$(CONFIG_TRACING) += tracefs.o >> >> diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c >> new file mode 100644 >> index 000000000..a48ce23c0 >> --- /dev/null >> +++ b/fs/tracefs/event_inode.c >> @@ -0,0 +1,272 @@ >> +// SPDX-License-Identifier: GPL-2.0-only >> +/* >> + * event_inode.c - part of tracefs, a pseudo file system for activating tracing >> + * >> + * Copyright (C) 2020-22 VMware Inc, author: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> >> + * Copyright (C) 2020-22 VMware Inc, author: Ajay Kaher <akaher@xxxxxxxxxx> >> + * >> + * eventfs is used to show trace events with one set of dentries >> + * >> + * eventfs stores meta-data of files/dirs and skip to create object of >> + * inodes/dentries. As and when requires, eventfs will create the >> + * inodes/dentries for only required files/directories. Also eventfs >> + * would delete the inodes/dentries once no more requires but preserve >> + * the meta data. >> + */ >> +#include <linux/fsnotify.h> >> +#include <linux/fs.h> >> +#include <linux/namei.h> >> +#include <linux/security.h> >> +#include <linux/tracefs.h> >> +#include <linux/kref.h> >> +#include <linux/delay.h> >> +#include "internal.h" >> + >> +/** >> + * eventfs_dentry_to_rwsem - Return corresponding eventfs_rwsem >> + * @dentry: a pointer to dentry >> + * >> + * helper function to return crossponding eventfs_rwsem for given dentry >> + */ >> +static struct rw_semaphore *eventfs_dentry_to_rwsem(struct dentry *dentry) >> +{ >> + if (S_ISDIR(dentry->d_inode->i_mode)) >> + return (struct rw_semaphore *)dentry->d_inode->i_private; >> + else >> + return (struct rw_semaphore *)dentry->d_parent->d_inode->i_private; >> +} >> + >> +/** >> + * eventfs_down_read - acquire read lock function >> + * @eventfs_rwsem: a pointer to rw_semaphore >> + * >> + * helper function to perform read lock. Nested locking requires because >> + * lookup(), release() requires read lock, these could be called directly >> + * or from open(), remove() which already hold the read/write lock. >> + */ >> +static void eventfs_down_read(struct rw_semaphore *eventfs_rwsem) >> +{ >> + down_read_nested(eventfs_rwsem, SINGLE_DEPTH_NESTING); >> +} >> + >> +/** >> + * eventfs_up_read - release read lock function >> + * @eventfs_rwsem: a pointer to rw_semaphore >> + * >> + * helper function to release eventfs_rwsem lock if locked >> + */ >> +static void eventfs_up_read(struct rw_semaphore *eventfs_rwsem) >> +{ >> + up_read(eventfs_rwsem); >> +} >> + >> +/** >> + * eventfs_down_write - acquire write lock function >> + * @eventfs_rwsem: a pointer to rw_semaphore >> + * >> + * helper function to perform write lock on eventfs_rwsem >> + */ >> +static void eventfs_down_write(struct rw_semaphore *eventfs_rwsem) >> +{ >> + while (!down_write_trylock(eventfs_rwsem)) >> + msleep(10); > > What's this loop for? Something like that needs a very good explanation > in a comment. Loops like these are usually a sign of a workaround for a > bug in the design, or worse, simply hides an existing bug. > Yes correct, this logic is to solve deadlock: Thread 1 Thread 2 down_read_nested() - read lock acquired down_write() - waiting for write lock to acquire down_read_nested() - deadlock Deadlock is because rwlock wouldn’t allow read lock to be acquired if write lock is waiting. down_write_trylock() wouldn’t add the write lock in waiting queue, hence helps to prevent deadlock scenario. I was stuck with this Deadlock, tried few methods and finally borrowed from cifs, as it’s upstreamed, tested and working in cifs, please refer: https://elixir.bootlin.com/linux/v6.3.1/source/fs/cifs/file.c#L438 Looking further for your input. I will add explanation in v4. >> +} >> + >> +/** >> + * eventfs_up_write - release write lock function >> + * @eventfs_rwsem: a pointer to rw_semaphore >> + * >> + * helper function to perform write lock on eventfs_rwsem >> + */ >> +static void eventfs_up_write(struct rw_semaphore *eventfs_rwsem) >> +{ >> + up_write(eventfs_rwsem); >> +} >> + >> +static const struct file_operations eventfs_file_operations = { >> +}; >> + >> +static const struct inode_operations eventfs_root_dir_inode_operations = { >> +}; >> + >> +/** >> + * eventfs_prepare_ef - helper function to prepare eventfs_file >> + * @name: a pointer to a string containing the name of the file/directory >> + * to create. >> + * @mode: the permission that the file should have. >> + * @fop: a pointer to a struct file_operations that should be used for >> + * this file/directory. >> + * @iop: a pointer to a struct inode_operations that should be used for >> + * this file/directory. >> + * @data: a pointer to something that the caller will want to get to later >> + * on. The inode.i_private pointer will point to this value on >> + * the open() call. >> + * >> + * This function allocate the fill eventfs_file structure. > > "allocates and fills the" ? > >> + */ >> +static struct eventfs_file *eventfs_prepare_ef(const char *name, umode_t mode, >> + const struct file_operations *fop, >> + const struct inode_operations *iop, >> + void *data) >> +{ >> + struct eventfs_file *ef; >> + >> + ef = kzalloc(sizeof(*ef), GFP_KERNEL); >> + if (!ef) >> + return ERR_PTR(-ENOMEM); >> + >> + ef->name = kstrdup(name, GFP_KERNEL); >> + if (!ef->name) { >> + kfree(ef); >> + return ERR_PTR(-ENOMEM); >> + } >> + >> + if (S_ISDIR(mode)) { >> + ef->ei = kzalloc(sizeof(*ef->ei), GFP_KERNEL); >> + if (!ef->ei) { >> + kfree(ef->name); >> + kfree(ef); >> + return ERR_PTR(-ENOMEM); >> + } >> + INIT_LIST_HEAD(&ef->ei->e_top_files); >> + } else { >> + ef->ei = NULL; >> + } >> + >> + ef->iop = iop; >> + ef->fop = fop; >> + ef->mode = mode; >> + ef->data = data; >> + ef->dentry = NULL; >> + ef->d_parent = NULL; >> + ef->created = false; > > No need for the initialization to NULL or even the false, as the > kzalloc() already did that. > >> + return ef; >> +} >> + >> +/** >> + * eventfs_create_events_dir - create the trace event structure >> + * @name: a pointer to a string containing the name of the directory to >> + * create. > > You don't need to add "a pointer" we can see it's a pointer. Just say: > > * @name: The name of the directory to create > > Adding more makes it confusing to read. > >> + * @parent: a pointer to the parent dentry for this file. This should be a >> + * directory dentry if set. If this parameter is NULL, then the >> + * directory will be created in the root of the tracefs filesystem. >> + * @eventfs_rwsem: a pointer to rw_semaphore > > Same with all the descriptions. > > >> + * >> + * This function creates the top of the trace event directory. >> + */ >> +struct dentry *eventfs_create_events_dir(const char *name, >> + struct dentry *parent, >> + struct rw_semaphore *eventfs_rwsem) > > OK, I'm going to have to really look at this. Passing in a lock to the > API is just broken. We need to find a way to solve this another way. eventfs_rwsem is a member of struct trace_array, I guess we should pass pointer to trace_array. > I'm about to board a plane to JFK shortly, I'm hoping to play with this > while flying back. > I have replied for major concerns. All other minor I will take care in v4. Thanks a lot for giving time to eventfs patches. - Ajay > -- Steve > > >> +{ >> + struct dentry *dentry = tracefs_start_creating(name, parent); >> + struct eventfs_inode *ei; >> + struct tracefs_inode *ti; >> + struct inode *inode; >> + >> + if (IS_ERR(dentry)) >> + return dentry; >> + >> + ei = kzalloc(sizeof(*ei), GFP_KERNEL); >> + if (!ei) >> + return ERR_PTR(-ENOMEM); >> + inode = tracefs_get_inode(dentry->d_sb); >> + if (unlikely(!inode)) { >> + kfree(ei); >> + tracefs_failed_creating(dentry); >> + return ERR_PTR(-ENOMEM); >> + } >> + >> + init_rwsem(eventfs_rwsem); >> + INIT_LIST_HEAD(&ei->e_top_files); >> + >> + ti = get_tracefs(inode); >> + ti->flags |= TRACEFS_EVENT_INODE; >> + ti->private = ei; >> + >> + inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO; >> + inode->i_op = &eventfs_root_dir_inode_operations; >> + inode->i_fop = &eventfs_file_operations; >> + inode->i_private = eventfs_rwsem; >> + >> + /* directory inodes start off with i_nlink == 2 (for "." entry) */ >> + inc_nlink(inode); >> + d_instantiate(dentry, inode); >> + inc_nlink(dentry->d_parent->d_inode); >> + fsnotify_mkdir(dentry->d_parent->d_inode, dentry); >> + return tracefs_end_creating(dentry); >> +} > > !! 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