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To: Jan Kara Cc: linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, gfs2@lists.linux.dev, linux-security-module@vger.kernel.org, agruenba@redhat.com, mic@digikod.net, gnoack@google.com, paul@paul-moore.com, jmorris@namei.org, serge@hallyn.com, aleksa@amutable.com, legion@kernel.org, djwong@kernel.org, ebiggers@kernel.org, sandeen@redhat.com References: <20260909090112.790006-1-sunjunchao@bytedance.com> <20260909090112.790006-3-sunjunchao@bytedance.com> From: Julian Sun In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/11/26 1:47 AM, Jan Kara wrote: > On Wed 09-09-26 17:01:07, Julian Sun wrote: >> Add sb_for_each_inodes() to share s_inodes traversal and preserve its >> position while s_inode_list_lock is dropped. >> >> Track active iterators on sb->s_inodes_iters and advance their saved >> positions before unlinking an inode. Callbacks manage inode references >> and per-inode work, allowing both normal walks and eviction to use the >> same interface. >> >> Signed-off-by: Julian Sun > > So I'm not generally opposed the to a superblock inode iterator idea but > what you have looks more complex than I'd expect. Also we shouldn't tie > that to the fix of the lockup in evict_inodes(). So first I'd just > concentrate on fixing that lockup, then we can have a look at the iterator > idea. > > You can take some inspiration about inode iteration API from the Dave > Chinner's patch set [1]. That looked more like what I'd expect although > Christoph had some comments on it too. > > Regarding the fix I'd just make evict_inodes() do what all other inode > iterators do when they decide to drop s_inode_list_lock - pin an inode in > the list by grabbing refcount and then resume from it. Thanks for the feedback. I agree that we should fix the lockup separately, and I'll focus on that first. I had seen Dave Chinner's series before. I'll revisit it and the review comments when working on the inode iteration API.> > Honza > > [1] https://lore.kernel.org/all/20241002014017.3801899-1-david@fromorbit.com/ > >> --- >> fs/inode.c | 93 ++++++++++++++++++++++++++++++++++ >> fs/super.c | 1 + >> include/linux/fs.h | 15 ++++++ >> include/linux/fs/super_types.h | 3 +- >> 4 files changed, 111 insertions(+), 1 deletion(-) >> >> diff --git a/fs/inode.c b/fs/inode.c >> index ba7da39be4a3..b4279063a5dd 100644 >> --- a/fs/inode.c >> +++ b/fs/inode.c >> @@ -69,6 +69,15 @@ const struct address_space_operations empty_aops = { >> }; >> EXPORT_SYMBOL(empty_aops); >> >> +struct inode_iter { >> + struct list_head iters_node; /* sb->s_inodes_iters */ >> + struct list_head *next; /* next node going to iterate */ >> + unsigned int flags; >> + inode_iter_cb func; >> + void *data; >> + int ret; >> +}; >> + >> static DEFINE_PER_CPU(unsigned long, nr_inodes); >> static DEFINE_PER_CPU(unsigned long, nr_unused); >> >> @@ -641,12 +650,96 @@ void inode_sb_list_add(struct inode *inode) >> } >> EXPORT_SYMBOL_GPL(inode_sb_list_add); >> >> +static void inode_sb_iter_start(struct super_block *sb, struct inode_iter *it, >> + unsigned int flags, inode_iter_cb fn, void *data) >> +{ >> + it->flags = flags; >> + it->func = fn; >> + it->data = data; >> + it->ret = 0; >> + spin_lock(&sb->s_inode_list_lock); >> + it->next = sb->s_inodes.next; >> + list_add(&it->iters_node, &sb->s_inodes_iters); >> +} >> + >> +static void inode_sb_iter_end(struct inode_iter *it, struct super_block *sb) >> +{ >> + list_del(&it->iters_node); >> + spin_unlock(&sb->s_inode_list_lock); >> +} >> + >> +static bool inode_sb_iter_next(struct inode_iter *it, struct super_block *sb) >> +{ >> + struct inode *inode = NULL; >> + int ret; >> + >> + while (!inode && it->next != &sb->s_inodes) { >> + inode = list_entry(it->next, struct inode, i_sb_list); >> + if (it->flags & INODE_ITER_UNUSED) { >> + if (icount_read_once(inode)) { >> + it->next = it->next->next; >> + continue; >> + } >> + >> + spin_lock(&inode->i_lock); >> + if (icount_read(inode)) { >> + spin_unlock(&inode->i_lock); >> + it->next = it->next->next; >> + continue; >> + } >> + } else { >> + spin_lock(&inode->i_lock); >> + } >> + >> + if ((it->flags & INODE_ITER_NORMAL) && >> + (inode_state_read(inode) & (I_NEW | I_FREEING | I_WILL_FREE))) { >> + spin_unlock(&inode->i_lock); >> + it->next = it->next->next; >> + continue; >> + } >> + >> + it->next = it->next->next; >> + ret = it->func(inode, it->data); >> + if (ret) { >> + it->ret = ret; >> + return false; >> + } >> + >> + if (need_resched()) { >> + spin_unlock(&sb->s_inode_list_lock); >> + cond_resched(); >> + spin_lock(&sb->s_inode_list_lock); >> + } >> + } >> + >> + return it->next == &sb->s_inodes ? false : true; >> +} >> + >> +int sb_for_each_inodes(struct super_block *sb, unsigned int flags, >> + inode_iter_cb fn, void *data) >> +{ >> + struct inode_iter it; >> + >> + inode_sb_iter_start(sb, &it, flags, fn, data); >> + while (inode_sb_iter_next(&it, sb)) >> + ; >> + inode_sb_iter_end(&it, sb); >> + >> + return it.ret; >> +} >> +EXPORT_SYMBOL(sb_for_each_inodes); >> + >> static inline void inode_sb_list_del(struct inode *inode) >> { >> struct super_block *sb = inode->i_sb; >> + struct inode_iter *it; >> >> if (!list_empty(&inode->i_sb_list)) { >> spin_lock(&sb->s_inode_list_lock); >> + list_for_each_entry(it, &sb->s_inodes_iters, iters_node) { >> + if (it->next == &inode->i_sb_list) >> + it->next = inode->i_sb_list.next; >> + } >> list_del_init(&inode->i_sb_list); >> spin_unlock(&sb->s_inode_list_lock); >> } >> diff --git a/fs/super.c b/fs/super.c >> index 05e443173038..3e069150c544 100644 >> --- a/fs/super.c >> +++ b/fs/super.c >> @@ -382,6 +382,7 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags, >> spin_lock_init(&s->s_roots_lock); >> mutex_init(&s->s_sync_lock); >> INIT_LIST_HEAD(&s->s_inodes); >> + INIT_LIST_HEAD(&s->s_inodes_iters); >> spin_lock_init(&s->s_inode_list_lock); >> INIT_LIST_HEAD(&s->s_inodes_wb); >> spin_lock_init(&s->s_inode_wblist_lock); >> diff --git a/include/linux/fs.h b/include/linux/fs.h >> index 09c4db5e9ae0..f3176ab10e65 100644 >> --- a/include/linux/fs.h >> +++ b/include/linux/fs.h >> @@ -870,6 +870,21 @@ struct inode { >> void *i_private; /* fs or device private pointer */ >> } __randomize_layout; >> >> +enum inode_iter_flags_enum { >> + INODE_ITER_NORMAL = (1U << 1), /* Exclude inodes with (I_NEW | I_FREEING | I_WILL_FREE). */ >> + INODE_ITER_UNUSED = (1U << 2), /* Only return inodes with (i_count == 0). */ >> +}; >> + >> +/* >> + * start end >> + * inode->i_lock locked unlocked >> + * sb->s_inode_list_lock locked locked >> + */ >> +typedef int (*inode_iter_cb) (struct inode *, void *); >> + >> +int sb_for_each_inodes(struct super_block *sb, unsigned int flags, >> + inode_iter_cb fn, void *data); >> + >> /* >> * i_state handling >> * >> diff --git a/include/linux/fs/super_types.h b/include/linux/fs/super_types.h >> index ecd96aeb1cee..1f81cc219b8e 100644 >> --- a/include/linux/fs/super_types.h >> +++ b/include/linux/fs/super_types.h >> @@ -269,9 +269,10 @@ struct super_block { >> */ >> int s_stack_depth; >> >> - /* s_inode_list_lock protects s_inodes */ >> + /* s_inode_list_lock protects s_inodes and s_inodes_iters */ >> spinlock_t s_inode_list_lock ____cacheline_aligned_in_smp; >> struct list_head s_inodes; /* all inodes */ >> + struct list_head s_inodes_iters; /* all iterators */ >> >> spinlock_t s_inode_wblist_lock; >> struct list_head s_inodes_wb; /* writeback inodes */ >> -- >> 2.39.5 >> Thanks, -- Julian Sun