Re: [PATCH V2 1/4] arm64/mm: Drop mmap_sem before calling __do_kernel_fault()

From: Catalin Marinas
Date: Tue Jun 04 2019 - 10:48:51 EST

On Mon, Jun 03, 2019 at 12:11:22PM +0530, Anshuman Khandual wrote:
> There is an inconsistency between down_read_trylock() success and failure
> paths while dealing with kernel access for non exception table areas where
> it calls __do_kernel_fault(). In case of failure it just bails out without
> holding mmap_sem but when it succeeds it does so while holding mmap_sem.
> Fix this inconsistency by just dropping mmap_sem in success path as well.
> __do_kernel_fault() calls die_kernel_fault() which then calls show_pte().
> show_pte() in this path might become bit more unreliable without holding
> mmap_sem. But there are already instances [1] in do_page_fault() where
> die_kernel_fault() gets called without holding mmap_sem. show_pte() can
> be made more robust independently but in a later patch.
> [1] Conditional block for (is_ttbr0_addr && is_el1_permission_fault)
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: James Morse <james.morse@xxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>

Queued for 5.3. Thanks.