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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776329532; bh=g1Hw4WC9BuiiYPxLoJGIqMt62pc+nYnQvs95d3Tl6IE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=SG1FGUNEpefy2PFt5pAPpydPb/RP3GVGwvaunJ/FzQfLwUhy55cvvCAZHOPqvXKpc I02KO1WCvxmiAZJBMYl5Cxmqx5wdgVKUN0SUb2yg8cK9h5NYsMKC/yH9NdjBJbzMbN fINLRueFjs6cPypk/vRCriX33RnKA6LsjX2g/pEtnbY6dpBQ62DbthA1HIrKSEob/A tg14TjjV4niiGvv+33alXBnmf9oSoRH+oMn+sG3cWlVLW6Cn25BPAfIaOwM09AWdzk 7cLESpUb2sdyMVI4S0oPe6QVEwB1AlVfnyisb0IEHEsj9j4MB47qI+eBntuo4hiSkR SOkkpg8Zohgmg== Message-ID: <7c5cffc5-f4db-490f-b8aa-6604c32b34f2@kernel.org> Date: Thu, 16 Apr 2026 10:52:05 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/zone_device: Do not touch device folio after calling ->folio_free() To: Alistair Popple , Matthew Brost Cc: intel-xe@lists.freedesktop.org, dri-devel@lists.freedesktop.org, Oscar Salvador , Andrew Morton , Balbir Singh , linux-mm@kvack.org, linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260410230346.4009855-1-matthew.brost@intel.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Stat-Signature: j4qcy6isdqjhwbqrfkeeodjwq7ja9qbd X-Rspam-User: X-Rspamd-Queue-Id: B1A1BC000D X-HE-Tag: 1776329533-870342 X-HE-Meta: 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 JgiFH7q1 Oi7+PS5aA/KQ1byWFZmktz5SXGWkZlwIJGev3Ef+jRUSfyw0W0GprJ6wBVc6MKn85V4TY9HecglWGdtx5PSPSJ99HhrJAAfQKdNIg6o7/vtDT12KzFcfIATwBkB5NpqMcXYYLRyv1Qnx+5ggIwfr0HWN6UMUTBMxvHnr5FY2lY9NctZrVw+nA2PIraQyjn8hcS/0jl5KHfZFXjhFEk5CPuh2xk1DOFeKtUBQ1sMn/FzUTQF61LYjH1qBE72au8QVmdHbojhVfuTepmI7sGupPCBONdfm9gEMoQu5KE9kc/SVY3nYHe6eTOiozX2rWnlEHz7CThbEqD4a3uRsKRAljo0nxtt2T4YI4wn0kvpFQtsNP6mSglOHjT8yRKrGpXYO7oy5pBVKaBzVrFypKsQvASqvlUTVr/iOSFZ9IdKL5I4ohDazM5HMqKouV495IDoINNWkaaDE1LullRNIDfzBu9SiVTy0vcaw4yM19yZiOg0z0iIhiOOFcivYeiA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/13/26 06:06, Alistair Popple wrote: > On 2026-04-11 at 09:03 +1000, Matthew Brost wrote... >> The contents of a device folio can immediately change after calling >> ->folio_free(), as the folio may be reallocated by a driver with a >> different order. Instead of touching the folio again to extract the >> pgmap, use the local stack variable when calling percpu_ref_put_many(). >> >> Cc: David Hildenbrand >> Cc: Oscar Salvador >> Cc: Andrew Morton >> Cc: Balbir Singh >> Cc: linux-mm@kvack.org >> Cc: linux-cxl@vger.kernel.org >> Cc: linux-kernel@vger.kernel.org >> Fixes: d245f9b4ab80 ("mm/zone_device: support large zone device private folios") >> Signed-off-by: Matthew Brost >> >> --- >> Stack trace: >> >> [ 631.875165] [IGT] xe_exec_system_allocator: starting subtest threads-many-new-prefetch >> [ 632.282992] Oops: general protection fault, probably for non-canonical address 0x900000000000000: 0000 [#1] SMP NOPTI >> [ 632.293469] CPU: 8 UID: 0 PID: 59267 Comm: xe_exec_system_ Not tainted 7.0.0-rc7-xe+ #281 PREEMPT(full) >> [ 632.316023] RIP: 0010:free_zone_device_folio+0x149/0x240 >> [ 632.339782] RSP: 0000:ffffc90023d1fd00 EFLAGS: 00010206 >> [ 632.344947] RAX: 0900000000000000 RBX: 0000000000000001 RCX: 0000000094472d4d >> [ 632.351991] RDX: ffffffff8155c76f RSI: 000000006f2213bf RDI: 000000008e84943a >> [ 632.359042] RBP: ffffea0ff4030001 R08: 0000000000000000 R09: 0000000000000001 >> [ 632.366094] R10: 0000000000000028 R11: 0000000000000000 R12: ffff88811828e400 >> [ 632.373145] R13: 0000000000000000 R14: 000fffffc0000000 R15: 0000000000100073 >> [ 632.380194] FS: 00007f2f0fdfe6c0(0000) GS:ffff88890a7e7000(0000) knlGS:0000000000000000 >> [ 632.388186] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> [ 632.393870] CR2: 00007f2f002e90f8 CR3: 0000000106708002 CR4: 0000000000f70ef0 >> [ 632.400919] PKRU: 55555554 >> [ 632.403605] Call Trace: >> [ 632.406039] >> [ 632.408131] do_swap_page+0x146d/0x18c0 >> [ 632.411938] ? __pte_offset_map+0x3e/0x190 >> [ 632.415994] __handle_mm_fault+0x6e8/0x8d0 >> [ 632.420053] handle_mm_fault+0xbf/0x250 >> [ 632.423855] ? lock_mm_and_find_vma+0x41/0x6f0 >> [ 632.428256] do_user_addr_fault+0x168/0x690 >> [ 632.432399] exc_page_fault+0x74/0x200 >> [ 632.436117] asm_exc_page_fault+0x26/0x30 >> [ 632.440092] RIP: 0033:0x5587554ff70d >> [ 632.462142] RSP: 002b:00007f2f0fdfc970 EFLAGS: 00010246 >> [ 632.467308] RAX: 0000000000003fc0 RBX: 00007f2f082e1fc0 RCX: 00007f2f12b3287d >> [ 632.474355] RDX: 0000000000000000 RSI: 00000000c048644a RDI: 0000000000000003 >> [ 632.481404] RBP: 00007f2f082e1fc0 R08: 00007f2f0fdfc958 R09: 0000000000000066 >> [ 632.488450] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001 >> [ 632.495495] R13: 00007f2f082de000 R14: 0000000000c00002 R15: 00007f2f1319e000 >> [ 632.502547] > > I'm not sure, but I think Andrew likes the stack traces included in the actual > commit messages. I've certainly found it helpful when debugging traces reported > from the field so would prefer it there. Agreed. > >> --- >> mm/memremap.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/memremap.c b/mm/memremap.c >> index ac7be07e3361..053842d45cb1 100644 >> --- a/mm/memremap.c >> +++ b/mm/memremap.c >> @@ -454,7 +454,7 @@ void free_zone_device_folio(struct folio *folio) >> if (WARN_ON_ONCE(!pgmap->ops || !pgmap->ops->folio_free)) >> break; >> pgmap->ops->folio_free(folio); >> - percpu_ref_put_many(&folio->pgmap->ref, nr); >> + percpu_ref_put_many(&pgmap->ref, nr); > I assume the ref keeps pgmap alive, such that that cannot go away after the folio_free(). Acked-by: David Hildenbrand (Arm) -- Cheers, David