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Date: Wed, 20 Feb 2019 09:01:24 +0100
From: Richard Weinberger <richard@...ma-star.at>
To: yuyufen <yuyufen@...wei.com>, dwmw2@...radead.org
Cc: richard.weinberger@...il.com, linux-mtd@...ts.infradead.org,
Joakim.Tjernlund@...inera.com, houtao1@...wei.com,
viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] jffs2: safely remove obsolete dirent from the f->dents list
Am Samstag, 16. Februar 2019, 09:53:35 CET schrieb yuyufen:
> ping?
Sorry for the delay.
I didn't forget (completely) about this one.
The thing is, I don't really maintain jffs2 but I will collect and test patches
for the upcoming merge window and carry them via my ubifs tree.
David, I hope I have by end of the week a list with potential patches ready
such that you can have a final look and veto what you don't like. :-)
Thanks,
//richard
>
> On 2019/1/23 15:22, Yufen Yu wrote:
> > We may delete a bunch of directory entries, operating such as:
> > getdents(), unlink(), getdents()..., until the end of the directory.
> > jffs2 handles f_pos on the directory merely as the position on the
> > f->dents list. So, the next getdents() may skip some entries
> > before f_pos, if we remove some entries from the list between two
> > getdents(), resulting in some entries of the directory cannot be deleted.
> >
> > Commit 15953580e79b is introduced to resolve this bug by not
> > removing delete entries from the list immediately.
> >
> > However, when CONFIG_JFFS2_SUMMARY is not set, it can cause the
> > following issues:
> >
> > * 'deletion' dirents is always in the f->dents list, wasting memory
> > resource. For example:
> > There is a file named 'file1'. Then we rename it:
> > mv file1 file2;
> > mv file2 file3;
> > ...
> > mv file99999 file1000000
> >
> > All of file1~file1000000 dirents always in the f->dents list.
> >
> > * Though, the list we're traversing is already ordered by CRC,
> > it could waste much CPU time when the list is very long.
> >
> > To fix, we define two variables in struct jffs2_inode_info: nr_dir_opening,
> > obsolete_count, and two new functions: jffs2_dir_open(), jffs2_dir_release().
> >
> > When open a directory, jffs2_dir_open() will increase nr_dir_opening,
> > which will be decreased by jffs2_dir_release(). if the value is 0,
> > it means nobody open the dir and nobody in getdents()/seek() semantics.
> > Thus, we can remove all obsolete dirent from the list.
> >
> > When delete a file, jffs2_do_unlink() can remove the dirent directly if
> > nobody open the directory(i.e. nr_dir_opending == 0). Otherwise, it just
> > increase obsolete_count, denoting obsolete dirent count of the list.
> >
> > Fixes: 15953580e79b ("[JFFS2] Improve getdents vs. f_pos handling on NOR flash.")
> > Signed-off-by: Yufen Yu <yuyufen@...wei.com>
> > ---
> > fs/jffs2/dir.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++
> > fs/jffs2/jffs2_fs_i.h | 7 +++++++
> > fs/jffs2/super.c | 4 ++++
> > fs/jffs2/write.c | 30 +++++++++++++++++++---------
> > include/uapi/linux/jffs2.h | 4 ++++
> > 5 files changed, 85 insertions(+), 9 deletions(-)
> >
> > diff --git a/fs/jffs2/dir.c b/fs/jffs2/dir.c
> > index f20cff1194bb..aed872dcd0ca 100644
> > --- a/fs/jffs2/dir.c
> > +++ b/fs/jffs2/dir.c
> > @@ -37,6 +37,8 @@ static int jffs2_mknod (struct inode *,struct dentry *,umode_t,dev_t);
> > static int jffs2_rename (struct inode *, struct dentry *,
> > struct inode *, struct dentry *,
> > unsigned int);
> > +static int jffs2_dir_release (struct inode *, struct file *);
> > +static int jffs2_dir_open (struct inode *, struct file *);
> >
> > const struct file_operations jffs2_dir_operations =
> > {
> > @@ -45,6 +47,8 @@ const struct file_operations jffs2_dir_operations =
> > .unlocked_ioctl=jffs2_ioctl,
> > .fsync = jffs2_fsync,
> > .llseek = generic_file_llseek,
> > + .open = jffs2_dir_open,
> > + .release = jffs2_dir_release,
> > };
> >
> >
> > @@ -865,3 +869,48 @@ static int jffs2_rename (struct inode *old_dir_i, struct dentry *old_dentry,
> > return 0;
> > }
> >
> > +static int jffs2_dir_open(struct inode *dir_i, struct file *filp)
> > +{
> > +#ifndef CONFIG_JFFS2_SUMMARY
> > + struct jffs2_inode_info *dir_f = JFFS2_INODE_INFO(dir_i);
> > + atomic_inc(&dir_f->nr_dir_opening);
> > +#endif
> > +
> > + return 0;
> > +}
> > +
> > +static int jffs2_dir_release(struct inode *dir_i, struct file *filp)
> > +{
> > +#ifndef CONFIG_JFFS2_SUMMARY
> > + struct jffs2_inode_info *dir_f = JFFS2_INODE_INFO(dir_i);
> > +
> > + BUG_ON(atomic_read(&dir_f->nr_dir_opening) <= 0);
> > +
> > + mutex_lock(&dir_f->sem);
> > + /* jffs2_dir_open may increase nr_dir_opening after
> > + * atomic_dec_and_test() returning true.
> > + * However, it cannot traverse the list until hold
> > + * mutex dir_f->sem lock, so that we can go on
> > + * removing.*/
> > + if (atomic_dec_and_test(&dir_f->nr_dir_opening) &&
> > + dir_f->obsolete_count > JFFS2_OBS_DIRENT_LIMIT) {
> > + struct jffs2_full_dirent **prev = &dir_f->dents;
> > +
> > + /* remove all obsolete dirent from the list, which
> > + * can save memory space and reduce CPU time for
> > + * traverse the list */
> > + while(*prev) {
> > + if ((*prev)->raw == NULL && (*prev)->ino == 0) {
> > + struct jffs2_full_dirent *this = *prev;
> > + *prev = this->next;
> > + jffs2_free_full_dirent(this);
> > + } else
> > + prev = &((*prev)->next);
> > + }
> > + dir_f->obsolete_count = 0;
> > + }
> > + mutex_unlock(&dir_f->sem);
> > +#endif
> > +
> > + return 0;
> > +}
> > diff --git a/fs/jffs2/jffs2_fs_i.h b/fs/jffs2/jffs2_fs_i.h
> > index 2e4a86763c07..a4da25d16cb4 100644
> > --- a/fs/jffs2/jffs2_fs_i.h
> > +++ b/fs/jffs2/jffs2_fs_i.h
> > @@ -50,6 +50,13 @@ struct jffs2_inode_info {
> >
> > uint16_t flags;
> > uint8_t usercompr;
> > +
> > + /* obsolete dirent count in the list of 'dents' */
> > + uint8_t obsolete_count;
> > +
> > + /* Directory open refcount */
> > + atomic_t nr_dir_opening;
> > +
> > struct inode vfs_inode;
> > };
> >
> > diff --git a/fs/jffs2/super.c b/fs/jffs2/super.c
> > index 87bdf0f4cba1..bf181b0ade9c 100644
> > --- a/fs/jffs2/super.c
> > +++ b/fs/jffs2/super.c
> > @@ -41,6 +41,10 @@ static struct inode *jffs2_alloc_inode(struct super_block *sb)
> > f = kmem_cache_alloc(jffs2_inode_cachep, GFP_KERNEL);
> > if (!f)
> > return NULL;
> > +
> > + atomic_set(&f->nr_dir_opening, 0);
> > + f->obsolete_count = 0;
> > +
> > return &f->vfs_inode;
> > }
> >
> > diff --git a/fs/jffs2/write.c b/fs/jffs2/write.c
> > index cda9a361368e..780b4fd9af51 100644
> > --- a/fs/jffs2/write.c
> > +++ b/fs/jffs2/write.c
> > @@ -600,29 +600,41 @@ int jffs2_do_unlink(struct jffs2_sb_info *c, struct jffs2_inode_info *dir_f,
> > } else {
> > uint32_t nhash = full_name_hash(NULL, name, namelen);
> >
> > - fd = dir_f->dents;
> > + struct jffs2_full_dirent **prev = &dir_f->dents;
> > +
> > /* We don't actually want to reserve any space, but we do
> > want to be holding the alloc_sem when we write to flash */
> > mutex_lock(&c->alloc_sem);
> > mutex_lock(&dir_f->sem);
> >
> > - for (fd = dir_f->dents; fd; fd = fd->next) {
> > - if (fd->nhash == nhash &&
> > - !memcmp(fd->name, name, namelen) &&
> > - !fd->name[namelen]) {
> > + while((*prev) && (*prev)->nhash <= nhash) {
> > + if ((*prev)->nhash == nhash &&
> > + !memcmp((*prev)->name, name, namelen) &&
> > + !(*prev)->name[namelen]) {
> >
> > + fd = *prev;
> > jffs2_dbg(1, "Marking old dirent node (ino #%u) @%08x obsolete\n",
> > fd->ino, ref_offset(fd->raw));
> > jffs2_mark_node_obsolete(c, fd->raw);
> > - /* We don't want to remove it from the list immediately,
> > - because that screws up getdents()/seek() semantics even
> > - more than they're screwed already. Turn it into a
> > - node-less deletion dirent instead -- a placeholder */
> > fd->raw = NULL;
> > fd->ino = 0;
> > +
> > + /* if nr_dir_openning is 0, we think nobody open the dir, and
> > + * nobody being in getdents()/seek() semantics. Thus, we can
> > + * safely remove this obsolete dirent from the list. Otherwise,
> > + * we just increase obsolete_count, and finally delete it in
> > + * jffs2_dir_release() */
> > + if (atomic_read(&dir_f->nr_dir_opening) == 0) {
> > + *prev = fd->next;
> > + jffs2_free_full_dirent(fd);
> > + } else
> > + dir_f->obsolete_count++;
> > +
> > break;
> > }
> > + prev = &((*prev)->next);
> > }
> > +
> > mutex_unlock(&dir_f->sem);
> > }
> >
> > diff --git a/include/uapi/linux/jffs2.h b/include/uapi/linux/jffs2.h
> > index a18b719f49d4..dff3ac2d6b0c 100644
> > --- a/include/uapi/linux/jffs2.h
> > +++ b/include/uapi/linux/jffs2.h
> > @@ -35,6 +35,10 @@
> > */
> > #define JFFS2_MAX_NAME_LEN 254
> >
> > +/* The obsolete dirent of dents list limit. When the number over
> > + * this limit, we can remove the obsoleted dents. */
> > +#define JFFS2_OBS_DIRENT_LIMIT 64
> > +
> > /* How small can we sensibly write nodes? */
> > #define JFFS2_MIN_DATA_LEN 128
> >
>
>
>
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