On Thu, Aug 10, 2023 at 8:12 PM Yu Zhao <yuzhao@xxxxxxxxxx> wrote: > > On Thu, Aug 10, 2023 at 5:46 PM Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote: > > > > On Thu, Aug 10, 2023 at 4:44 PM Yu Zhao <yuzhao@xxxxxxxxxx> wrote: > > > > > > On Thu, Aug 10, 2023 at 5:31 PM Yin, Fengwei <fengwei.yin@xxxxxxxxx> wrote: > > > > > > > > > > > > > > > > On 8/11/2023 7:15 AM, Yosry Ahmed wrote: > > > > > On Thu, Aug 10, 2023 at 4:09 PM Yin, Fengwei <fengwei.yin@xxxxxxxxx> wrote: > > > > >> > > > > >> > > > > >> > > > > >> On 8/11/2023 2:44 AM, Yu Zhao wrote: > > > > >>> On Thu, Aug 10, 2023 at 3:58 AM Yin Fengwei <fengwei.yin@xxxxxxxxx> wrote: > > > > >>>> > > > > >>>> With mm-unstable branch, if trigger swap activity and it's possible > > > > >>>> 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 + PIIX,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 a8 01 0f 84 84 04 00 00 48 89 df e8 d7 db ff ff 48 8b 00 a9 00 00 08 00 0f 85 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:ffff88813bc80000(0000) knlGS:0000000000000000 > > > > >>>> [ 178.116423][ T651] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > > > >>>> [ 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] <TASK> > > > > >>>> [ 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 folio > > > > >>>> 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. Thanks. > > > > > > > > > > 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. > > > > > > Please don't overegineer. > > > > How so? > > > > Using zswap with zram is a weird combination > > Not at all -- it can achieve tiering between different compressors: > fast but low compression ratio for zswap but the opposite for zram. That's definitely an interesting use case, thanks for pointing this out. I would prefer creating a helper and using it in both do_swap_fault() and zswap_load() in the WARN_ON (with data_race()), but I am not against just removing the WARN_ON either. I will leave it up to you and Yin :) > > > if anything I would > > prefer leaving the warning as-is than removing it to be honest.
