Messages in this thread |  | | Date | Mon, 10 Feb 2025 17:03:13 +0000 | | From | "Russell King (Oracle)" <> | | Subject | Re: [REGRESSION] NULL pointer dereference on ARM (AT91SAM9G25) during compaction |
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On Mon, Feb 10, 2025 at 05:49:38PM +0100, Ezra Buehler wrote: > When running vanilla Linux 6.13 or newer (6.14-rc2) on the > AT91SAM9G25-based GARDENA smart Gateway, we are seeing a NULL pointer > dereference resulting in a kernel panic. The culprit seems to be commit > fc9c45b71f43 ("arm: adjust_pte() usepte_offset_map_rw_nolock()"). > Reverting the commit apparently fixes the issue.
The blamed commit is buggy:
arch/arm/include/asm/tlbflush.h: #define update_mmu_cache(vma, addr, ptep) \ update_mmu_cache_range(NULL, vma, addr, ptep, 1)
So vmf can be NULL. This didn't used to matter before this commit, because vmf was not used by ARM's update_mmu_cache_range(). However, the commit introduced a dereference of it, which now causes a NULL point dereference.
Not sure what the correct solution is, but at a guess, both:
if (ptl != vmf->ptl)
need to become:
if (!vmf || ptl != vmf->ptl)
but I haven't checked wha tthe locking context actually is here (I've been out of MM stuff too long to know this off the top of my head.)
-- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
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