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
