Re: [PATCH v3 04/15] mm/memory-failure: convert process iterator to for_each_process_rculock

[Ye Liu <ye.liu@linux.dev>]

在 2026/9/11 16:13, sashiko-bot@kernel.org 写道:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> 
> Pre-existing issues:
> - [High] Potential NULL pointer dereference or Use-After-Free of `folio->mapping` in `collect_procs_file()` due to concurrent truncation.
> --
> 
Unrelated to this patch. I will fix it later.

> commit 788d1f422c3f19026d9e0d86b550c238607720ed
> Author: Ye Liu <liuye@kylinos.cn>
> 
> mm/memory-failure: convert process iterator to for_each_process_rculock
> 
> This commit replaces the manual rcu_read_lock()/rcu_read_unlock() pairs
> combined with for_each_process() loop in mm/memory-failure.c with
> for_each_process_rculock(), which scopes the RCU read lock to the loop body
> via scoped_guard(rcu).
> 
>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>> index a8b03e2920ba8..7d93deb1f7b3d 100644
>> --- a/mm/memory-failure.c
>> +++ b/mm/memory-failure.c
> [ ... ]
>> @@ -589,9 +587,8 @@ static void collect_procs_file(const struct folio *folio,
>>  	pgoff_t pgoff;
>>  
>>  	i_mmap_lock_read(mapping);
> 
> [Severity: High]
> This is a pre-existing issue, but could this lead to a NULL pointer
> dereference or a use-after-free of mapping due to a race with truncation?
> 
> In memory_failure(), the folio lock is dropped in hwpoison_user_mappings()
> before calling collect_procs(). collect_procs() performs an unlocked check of
> !folio->mapping:
> 
> static void collect_procs(...)
> {
> 	if (!folio->mapping)
> 		return;
> 	...
> 	else
> 		collect_procs_file(folio, page, tokill, force_early);
> }
> 
> If a concurrent truncation removes the folio from the page cache immediately
> after this check, folio->mapping becomes NULL. collect_procs_file() then
> initializes mapping = folio->mapping and calls i_mmap_lock_read(mapping).
> 
> If the compiler performs a second read of folio->mapping, mapping will be
> NULL, crashing the kernel on the semaphore acquisition. If the compiler
> caches the first read, mapping will point to an address_space whose host
> inode may have been concurrently freed, leading to a use-after-free since
> the elevated page refcount does not pin the inode and no RCU read lock is
> held during the blocking i_mmap_lock_read() call.
> 
>> -	rcu_read_lock();
>>  	pgoff = page_pgoff(folio, page);
>> -	for_each_process(tsk) {
>> +	for_each_process_rculock(tsk) {
>>  		struct task_struct *t = task_early_kill(tsk, force_early);
>>  		unsigned long addr;
> 

-- 
Thanks,
Ye Liu