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 V/meIp3B 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000304, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Just looking at this and the backtrace: > On Apr 12, 2023, at 09:14, Matthew Wilcox wrote: >=20 > On Tue, Apr 11, 2023 at 05:15:36PM -0700, Andrew Morton wrote: >> On Tue, 11 Apr 2023 13:16:18 +0100 Matthew Wilcox = wrote: >>=20 >>> On Mon, Apr 10, 2023 at 09:45:02AM +0800, xiaosong.ma wrote: >>>> perform the check in dump_mapping() to print warning info and avoid cr= ash with invalid non-NULL page->mapping. >>>> For example, a panic with following backtraces show dump_page will sho= w wrong info and panic when the bad page >>>> is non-NULL mapping and page->mapping is 0x80000000000. >>>>=20 >>>> crash_arm64> bt >>>> PID: 232 TASK: ffffff80e8c2c340 CPU: 0 COMMAND: "Binder:232_2= " >>>> #0 [ffffffc013e5b080] sysdump_panic_event$b2bce43a479f4f7762201bfe= e02d7889 at ffffffc0108d7c2c >>>> #1 [ffffffc013e5b0c0] atomic_notifier_call_chain at ffffffc0103002= 28 >>>> #2 [ffffffc013e5b2c0] panic at ffffffc0102c926c >>>> #3 [ffffffc013e5b370] die at ffffffc010267670 >>>> #4 [ffffffc013e5b3a0] die_kernel_fault at ffffffc0102808a4 >>>> #5 [ffffffc013e5b3d0] __do_kernel_fault at ffffffc010280820 >>>> #6 [ffffffc013e5b410] do_bad_area at ffffffc01028059c >>>> #7 [ffffffc013e5b440] do_translation_fault$4df5decbea5d08a63349aa3= 6f07426b2 at ffffffc0111149c8 >>>> #8 [ffffffc013e5b470] do_mem_abort at ffffffc0100a4488 >>>> #9 [ffffffc013e5b5e0] el1_ia at ffffffc0100a6c00 >>>> #10 [ffffffc013e5b5f0] __dump_page at ffffffc0104beecc >>>=20 >>> This doesn't show a crash in dump_mapping(), it shows a crash in >>> __dump_page(). >>=20 >> um, yes. >>=20 >> But if page->mapping is corrupted, where does __dump_page() dereference = it? >=20 > I don't see anywhere that it does, so I'm suspicious that we have the > correct diagnosis here. I agree; since dump_mapping() is an actual function rather than a macro or inline, if a bad dereference were happening within dump_mapping() I would t= hink we SHOULD see the call to dump_mapping() on the stack unless I'm missing something obvious here. Instead I'd like to know which instruction the faulting address in __dump_p= age() maps to for the kernel experiencing this. >> The initial patch >> (https://lkml.kernel.org/r/1680587425-4683-1-git-send-email-Xiaosong.Ma@= unisoc.com) >> prevented __dump_page() from calling dump_mapping() if page->mapping is >> bad, and that presumably fixed things. >=20 > Right, but doesn't the _existing_ get_kernel_nofault(host, &mapping->host= ) > already prevent us from blindly dereferencing a bad mapping pointer? I would think it would, but given the traceback, is the fault occurring within dump_mapping(), or have we perhaps completed dump_mapping() and some subtle corruption occurred such that the fault occurs on the return to __dump_page()? Certainly dump_mapping() looks to do the right thing to avoid using a bad passed "mapping" as it's not dereferenced anywhere without checks, just used for pointer math to create an address for calls to get_kernel_notfault= (). >> So confusion reigns. I think making dump_mapping() tolerant of a wild >> mapping pointer makes sense, but I don't think we actually know why the >> reporter's kernel crashed. >=20 > In my mind dump_mapping() is already tolerant of a wild page->mapping > pointer. I think the problem is something entirely different. Again, I agree. As posited above, could it be that something occurs within dump_mapping() such that when the code returns to __dump_page() it is at THAT point that the fault occurs? That would explain the backtrace and why it shows the fault as occurring within __dump_page(), but upon first glance the mechanism by which this could be occurring eludes me. The original patch doesn't mention whether any pr_warn() messages were printed as a result of the call to dump_mapping(), and the suggested fix would fix the issue whether the fault were occurring within dump_mapping() = or in the return from calling dump_mapping(). -- Bill