Re: [PATCH] fs: rotate inodes whose page cache could not be dropped

[Zhihao Cheng <chengzhihao1@huawei.com>]

在 2026/10/19 16:50, Nick Karaolidis 写道:
> On Saturday, October 17th, 2026 at 8:43 AM, Zhihao Cheng <chengzhihao1@huawei.com> wrote:
> 
>> Hi Nikolaos,
>> I find a possible BUG_ON if this patch applied, details shown as:
>>      P1                          P2
>> prune_icache_sb
>>    lock(lru->lock)
>>    inode_lru_isolate
>>     if (!mapping_empty(&inode->i_data))
>>      unlock(lru->lock)
>>      spin_lock(&inode->i_lock)
>>      inode_state_set(inode, I_REFERENCED)
>>      inode_unpin_lru_isolating
>>      spin_unlock(&inode->i_lock)
>>                            unlink
>>                             iget_locked // find_inode_fast gets the inode
>>                             iput
>>                              iput_final
>>                               drop = 1
>>                               evict
>>                                BUG_ON(inode_state_read_once(inode) !=
>> (I_FREEING | I_CLEAR))  // inode state with I_REFERENCED
>>
>> Could that be possible?
> 
> Hi Zhihao,
> 
> Thanks for looking at this. I don't think that BUG_ON can trigger.
> 
> - The patch sets I_REFERENCED in the same i_lock section that clears
>    I_LRU_ISOLATING, and evict() waits in inode_wait_for_lru_isolating()
>    before calling ->evict_inode(), so the walker can only set the flag
>    before the filesystem's eviction runs.
> 
> - clear_inode(), which every ->evict_inode() calls, sets i_state to
>    I_FREEING | I_CLEAR.
OK, I missunderstand the realization of 'inode_state_assign_raw(inode, 
I_FREEING | I_CLEAR)' in the clear_inode().
> 
> - Evicting an inode that has I_REFERENCED set already happens.
>    iput_final() sets it through __inode_lru_list_add(inode, true) when
>    the inode is already on the LRU.
> 
> Did I miss a path that checks i_state before clear_inode()?
> 
> Thanks,
> Nikolaos
> 
> .
>