lkml.org 
[lkml]   [2021]   [Dec]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] mm: delete unsafe BUG from page_cache_add_speculative()
On Wed, 8 Dec 2021 23:19:18 -0800 (PST) Hugh Dickins <hughd@google.com> wrote:

> It is not easily reproducible, but on 5.16-rc I have several times hit
> the VM_BUG_ON_PAGE(PageTail(page), page) in page_cache_add_speculative():
> usually from filemap_get_read_batch() for an ext4 read, yesterday from
> next_uptodate_page() from filemap_map_pages() for a shmem fault.
>
> That BUG used to be placed where page_ref_add_unless() had succeeded,
> but now it is placed before folio_ref_add_unless() is attempted: that
> is not safe, since it is only the acquired reference which makes the
> page safe from racing THP collapse or split.
>
> We could keep the BUG, checking PageTail only when folio_ref_try_add_rcu()
> has succeeded; but I don't think it adds much value - just delete it.
>
> Fixes: 020853b6f5ea ("mm: Add folio_try_get_rcu()")
> Signed-off-by: Hugh Dickins <hughd@google.com>

I added cc:stable to this.

\
 
 \ /
  Last update: 2021-12-10 18:20    [W:0.072 / U:1.328 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site