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10 Aug 2023 21:02:55 -0600 Message-ID: Subject: Re: [PATCH] zswap: don't warn if none swapcache folio is passed to zswap_load To: "Yin, Fengwei" Cc: Yosry Ahmed , linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, willy@infradead.org, hannes@cmpxchg.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: ba1sep1q9eo8aiss1ec1ameebryyoz8n X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: CE64E14000F X-Rspam-User: X-HE-Tag: 1691723012-832099 X-HE-Meta: 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 aW5QMY11 wm8SN1hwLbvQJmyahhBH5sw5slcdPmphLDqI40nbQ4opSg5EVLPvVjzKrQcnDTVS1uJxWRqzALjOx/5TenVd5ec5rA77N9MkQx9r6O0PVqz8mTLy9SwSuLxCpcAWO6V4CiUHOF+pbqyAkcpjbRAIIw9JYEsDquxYsiAot4BR890wUtKkvYu7KEfXPe9IW0+lWAneoaBcothQ98TUCRKCnXYbmF0jtriq53EDObPLA7kuwhRWz8jOwwQoySkhUc5LUy9G7551x6ZNSOY5gjg8+zOByRhqKDZoLJaeLF4igyFJt292TG53q8M03ah5cYU1Ah/Vx5O3jjkFd8AQ= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Aug 10, 2023 at 6:37=E2=80=AFPM Yin, Fengwei wrote: > > > > On 8/11/2023 7:43 AM, Yu Zhao wrote: > > On Thu, Aug 10, 2023 at 5:31=E2=80=AFPM Yin, Fengwei wrote: > >> > >> > >> > >> On 8/11/2023 7:15 AM, Yosry Ahmed wrote: > >>> On Thu, Aug 10, 2023 at 4:09=E2=80=AFPM Yin, Fengwei wrote: > >>>> > >>>> > >>>> > >>>> On 8/11/2023 2:44 AM, Yu Zhao wrote: > >>>>> On Thu, Aug 10, 2023 at 3:58=E2=80=AFAM Yin Fengwei wrote: > >>>>>> > >>>>>> With mm-unstable branch, if trigger swap activity and it's possibl= e > >>>>>> see following warning: > >>>>>> [ 178.093511][ T651] WARNING: CPU: 2 PID: 651 at mm/zswap.c:1387= zswap_load+0x67/0x570 > >>>>>> [ 178.095155][ T651] Modules linked in: > >>>>>> [ 178.096103][ T651] CPU: 2 PID: 651 Comm: gmain Not tainted 6.5= .0-rc4-00492-gad3232df3e41 #148 > >>>>>> [ 178.098372][ T651] Hardware name: QEMU Standard PC (i440FX + P= IIX,1996), BIOS 1.14.0-2 04/01/2014 > >>>>>> [ 178.101114][ T651] RIP: 0010:zswap_load+0x67/0x570 > >>>>>> [ 178.102359][ T651] Code: a0 78 4b 85 e8 ea db ff ff 48 8b 00 a= 8 01 0f 84 84 04 00 00 48 89 df e8 d7 db ff ff 48 8b 00 a9 00 00 08 00 0f 8= 5 c4 > >>>>>> [ 178.106376][ T651] RSP: 0018:ffffc900011b3760 EFLAGS: 00010246 > >>>>>> [ 178.107675][ T651] RAX: 0017ffffc0080001 RBX: ffffea0004a991c0= RCX:ffffc900011b37dc > >>>>>> [ 178.109242][ T651] RDX: 0000000000000000 RSI: 0000000000000001= RDI:ffffea0004a991c0 > >>>>>> [ 178.110916][ T651] RBP: ffffea0004a991c0 R08: 0000000000000243= R09:00000000c9a1aafc > >>>>>> [ 178.112377][ T651] R10: 00000000c9657db3 R11: 000000003c9657db= R12:0000000000014b9c > >>>>>> [ 178.113698][ T651] R13: ffff88813501e710 R14: ffff88810d591000= R15:0000000000000000 > >>>>>> [ 178.115008][ T651] FS: 00007fb21a9ff700(0000) GS:ffff88813bc8= 0000(0000) knlGS:0000000000000000 > >>>>>> [ 178.116423][ T651] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080= 050033 > >>>>>> [ 178.117421][ T651] CR2: 00005632cbfc81f6 CR3: 0000000131450002= CR4:0000000000370ee0 > >>>>>> [ 178.118683][ T651] DR0: 0000000000000000 DR1: 0000000000000000= DR2:0000000000000000 > >>>>>> [ 178.119894][ T651] DR3: 0000000000000000 DR6: 00000000fffe0ff0= DR7:0000000000000400 > >>>>>> [ 178.121087][ T651] Call Trace: > >>>>>> [ 178.121654][ T651] > >>>>>> [ 178.122109][ T651] ? zswap_load+0x67/0x570 > >>>>>> [ 178.122658][ T651] ? __warn+0x81/0x170 > >>>>>> [ 178.123119][ T651] ? zswap_load+0x67/0x570 > >>>>>> [ 178.123608][ T651] ? report_bug+0x167/0x190 > >>>>>> [ 178.124150][ T651] ? handle_bug+0x3c/0x70 > >>>>>> [ 178.124615][ T651] ? exc_invalid_op+0x13/0x60 > >>>>>> [ 178.125192][ T651] ? asm_exc_invalid_op+0x16/0x20 > >>>>>> [ 178.125753][ T651] ? zswap_load+0x67/0x570 > >>>>>> [ 178.126231][ T651] ? lock_acquire+0xbb/0x290 > >>>>>> [ 178.126745][ T651] ? folio_add_lru+0x40/0x1c0 > >>>>>> [ 178.127261][ T651] ? find_held_lock+0x2b/0x80 > >>>>>> [ 178.127776][ T651] swap_readpage+0xc7/0x5c0 > >>>>>> [ 178.128273][ T651] do_swap_page+0x86d/0xf50 > >>>>>> [ 178.128770][ T651] ? __pte_offset_map+0x3e/0x290 > >>>>>> [ 178.129321][ T651] ? __pte_offset_map+0x1c4/0x290 > >>>>>> [ 178.129883][ T651] __handle_mm_fault+0x6ad/0xca0 > >>>>>> [ 178.130419][ T651] handle_mm_fault+0x18b/0x410 > >>>>>> [ 178.130992][ T651] do_user_addr_fault+0x1f1/0x820 > >>>>>> [ 178.132076][ T651] exc_page_fault+0x63/0x1a0 > >>>>>> [ 178.132599][ T651] asm_exc_page_fault+0x22/0x30 > >>>>>> > >>>>>> It's possible that swap_readpage() is called with none swapcache f= olio > >>>>>> in do_swap_page() and trigger this warning. So we shouldn't assume > >>>>>> zswap_load() always takes swapcache folio. > >>>>> > >>>>> Did you use a bdev with QUEUE_FLAG_SYNCHRONOUS? Otherwise it sounds > >>>>> like a bug to me. > >>>> I hit this warning with zram which has QUEUE_FLAG_SYNCHRONOUS set. T= hanks. > >>> > >>> Does it make sense to keep the warning and instead change it to check > >>> SWP_SYNCHRONOUS_IO as well? Something like: > >>> > >>> VM_WARN_ON_ONCE(!folio_test_swapcache(folio) && > >>> !swap_type_to_swap_info(type)->flags && SWP_SYNCHRONOUS_IO); > >>> > >>> Of course this is too ugly, so perhaps we want a helper to check if a > >>> swapfile is synchronous. > >> My understanding was that the WARN here is zswap_load() doesn't expect > >> a folio not in swapcache. With zram, swap_readpage() must accept the > >> folio not in swapcache. So this warn should not be there. > >> > >> But your comment make more sense to me. I will update the patch not > >> to remove this WARN. Thanks. > > > > That can cause another warning. > My understanding is that WARN may be wanted by zswap code. > > > > > Please don't overegineer. The original patch looks good to me. What Yosry suggested seems not only overengineered but also can cause a new KCSAN warning.