mm: lift gfp_kmemleak_mask() to gfp.h
Patch series "mm: fix nested allocation context filtering". This patchset is the followup to the comment I made earlier today: https://lore.kernel.org/linux-xfs/ZjAyIWUzDipofHFJ@dread.disaster.area/ Tl;dr: Memory allocations that are done inside the public memory allocation API need to obey the reclaim recursion constraints placed on the allocation by the original caller, including the "don't track recursion for this allocation" case defined by __GFP_NOLOCKDEP. These nested allocations are generally in debug code that is tracking something about the allocation (kmemleak, KASAN, etc) and so are allocating private kernel objects that only that debug system will use. Neither the page-owner code nor the stack depot code get this right. They also also clear GFP_ZONEMASK as a separate operation, which is completely redundant because the constraint filter applied immediately after guarantees that GFP_ZONEMASK bits are cleared. kmemleak gets this filtering right. It preserves the allocation constraints for deadlock prevention and clears all other context flags whilst also ensuring that the nested allocation will fail quickly, silently and without depleting emergency kernel reserves if there is no memory available. This can be made much more robust, immune to whack-a-mole games and the code greatly simplified by lifting gfp_kmemleak_mask() to include/linux/gfp.h and using that everywhere. Also document it so that there is no excuse for not knowing about it when writing new debug code that nests allocations. Tested with lockdep, KASAN + page_owner=on and kmemleak=on over multiple fstests runs with XFS. This patch (of 3): Any "internal" nested allocation done from within an allocation context needs to obey the high level allocation gfp_mask constraints. This is necessary for debug code like KASAN, kmemleak, lockdep, etc that allocate memory for saving stack traces and other information during memory allocation. If they don't obey things like __GFP_NOLOCKDEP or __GFP_NOWARN, they produce false positive failure detections. kmemleak gets this right by using gfp_kmemleak_mask() to pass through the relevant context flags to the nested allocation to ensure that the allocation follows the constraints of the caller context. KASAN recently was foudn to be missing __GFP_NOLOCKDEP due to stack depot allocations, and even more recently the page owner tracking code was also found to be missing __GFP_NOLOCKDEP support. We also don't wan't want KASAN or lockdep to drive the system into OOM kill territory by exhausting emergency reserves. This is something that kmemleak also gets right by adding (__GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN) to the allocation mask. Hence it is clear that we need to define a common nested allocation filter mask for these sorts of third party nested allocations used in debug code. So to start this process, lift gfp_kmemleak_mask() to gfp.h and rename it to gfp_nested_mask(), and convert the kmemleak callers to use it. Link: https://lkml.kernel.org/r/20240430054604.4169568-1-david@fromorbit.com Link: https://lkml.kernel.org/r/20240430054604.4169568-2-david@fromorbit.com Signed-off-by:Dave Chinner <dchinner@redhat.com> Reviewed-by:
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