On (24/02/27 10:04), Andrew Morton wrote: > The patch titled > Subject: mm/zsmalloc: don't hold locks of all pages when free_zspage() > has been added to the -mm mm-unstable branch. Its filename is > mm-zsmalloc-dont-hold-locks-of-all-pages-when-free_zspage.patch > > This patch will shortly appear at > https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-zsmalloc-dont-hold-locks-of-all-pages-when-free_zspage.patch > > This patch will later appear in the mm-unstable branch at > git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm > > Before you just go and hit "reply", please: > a) Consider who else should be cc'ed > b) Prefer to cc a suitable mailing list as well > c) Ideally: find the original patch on the mailing list and do a > reply-to-all to that, adding suitable additional cc's > > *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** > > The -mm tree is included into linux-next via the mm-everything > branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm > and is updated there every 2-3 working days > > ------------------------------------------------------ > From: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx> > Subject: mm/zsmalloc: don't hold locks of all pages when free_zspage() > Date: Tue, 27 Feb 2024 03:02:54 +0000 > > Patch series "mm/zsmalloc: simplify synchronization between > zs_page_migrate() and free_zspage()". > > free_zspage() has to hold locks of all pages, since zs_page_migrate() path > rely on this page lock to protect the race between zs_free() and it, so it > can safely get zspage from page->private. > > But this way is not good and simple enough: > > 1. Since zs_free() couldn't be sleepable, it can only trylock pages, > or has to kick_deferred_free() to defer that to a work. > > 2. Even in the worker context, async_free_zspage() can't simply > lock all pages in lock_zspage(), it's still trylock because of > the race between zs_free() and zs_page_migrate(). Please see > the commit 2505a981114d ("zsmalloc: fix races between asynchronous > zspage free and page migration") for details. > > Actually, all free_zspage() needs is to get zspage from page safely, we > can use RCU to achieve it easily. Then free_zspage() don't need to hold > locks of all pages, so don't need the deferred free mechanism at all. > This patchset implements it and remove all of deferred free related code. > > > This patch (of 2): > > free_zspage() has to hold locks of all pages, since zs_page_migrate() path > rely on this page lock to protect the race between zs_free() and it, so it > can safely get zspage from page->private. Andrew, please drop this series as it's NULL-deref crashing zsmalloc (as far as I can tell).
