Messages in this thread | | | Date | Tue, 3 Oct 2023 22:12:29 +0200 | Subject | Re: BUG: KCSAN: data-race in folio_batch_move_lru / mpage_read_end_io | From | Mirsad Todorovac <> |
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On 9/18/23 16:53, Matthew Wilcox wrote: > On Mon, Sep 18, 2023 at 02:15:05PM +0200, Mirsad Todorovac wrote: >>> This is what I'm currently running with, and it doesn't trigger. >>> I'd expect it to if we were going to hit the KCSAN bug. >>> >>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>> index 0c5be12f9336..d22e8798c326 100644 >>> --- a/mm/page_alloc.c >>> +++ b/mm/page_alloc.c >>> @@ -4439,6 +4439,7 @@ struct page *__alloc_pages(gfp_t gfp, unsigned int order, int preferred_nid, >>> page = __alloc_pages_slowpath(alloc_gfp, order, &ac); >>> out: >>> + VM_BUG_ON_PAGE(page && (page->flags & (PAGE_FLAGS_CHECK_AT_PREP &~ (1 << PG_head))), page); >>> if (memcg_kmem_online() && (gfp & __GFP_ACCOUNT) && page && >>> unlikely(__memcg_kmem_charge_page(page, gfp, order) != 0)) { >>> __free_pages(page, order); >> >> Hi, >> >> Caught another instance of this bug involving folio_batch_move_lru: I don't seem that I can make it >> happen reliably by the nature of the data racing conditions if I understood them well. > > Were you running with this patch at the time, or was this actually > vanilla? The problem is that, if my diagnosis is correct, both of the > tasks mentioned are victims; we have a prematurely freed page. While > btrfs is clearly a user, it may not be btrfs's fault that the > page was also allocated as an anon page. > > I'm trying to gather more data, and running with this patch will give > us more -- because it'll dump the entire struct page instead of just > the page->flags, like KCSAN is currently doing.
As my learning curve adapts, I seem to be more aware of what you are talking about.
I still have to learn to cope with patches, diffs, fixes and pulls all together and consistent.
Sometimes I feel like in the BORG maturation chamber when I try to learn the Linux kernel, and I wonder if this is the Author of my story trying to make up "for the years that locust had eaten". Or is it that I am just losing the plot.
I learn that I was conceited and not respecting the work you guys have done in thirty years I wasted for one reason or another: objective difficulties and personal weaknesses.
Forgive me this moment of truth.
I certainly feel more motivated to catch the real culprit, rather than just the symptoms.
I will rebuild with your patch again and try to reproduce the problem.
Best regards Mirsad Todorovac
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