If zram supports writeback feature, it's no more syncrhonous device beause zram does synchronous IO opeation for incompressible page. Do not pretend to be syncrhonous IO device. It makes system very sluggish as waiting IO completion from upper layer. Furthermore, it makes user-after-free problem because swap think the opearion is done when the IO functions returns so it could free page by will(e.g., lock_page_or_retry and goto out_release in do_swap_page) but in fact, IO is asynchrnous so driver could access just freed page afterward. This patch fixes the problem. BUG: Bad page state in process qemu-system-x86 pfn:3dfab21 page:ffffdfb137eac840 count:0 mapcount:0 mapping:0000000000000000 index:0x1 flags: 0x17fffc000000008(uptodate) raw: 017fffc000000008 dead000000000100 dead000000000200 0000000000000000 raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000 page dumped because: PAGE_FLAGS_CHECK_AT_PREP flag set bad because of flags: 0x8(uptodate) Modules linked in: lz4 lz4_compress zram zsmalloc intel_rapl sb_edac x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm irqbypass crct10dif_pclmul crc32_pclmul ghash_clmulni_intel bin fmt_misc pcbc aesni_intel aes_x86_64 crypto_simd cryptd iTCO_wdt glue_helper iTCO_vendor_support intel_cstate lpc_ich mei_me intel_uncore intel_rapl_perf pcspkr joydev sg mfd_core ioatdma mei wmi evdev ipmi_si ipmi_devintf ipmi_msghandler acpi_power_meter acpi_pad button ip_tables x_tables autofs4 ext4 crc32c_generic crc16 mbcache jbd2 fscrypto hid_generic usbhid hid sd_mod xhci_pci ehci_pci ahci libahci xhci_hcd ehci_hcd libata igb i2c_algo_bit crc32c_intel scsi_mod i2c_i8 01 dca usbcore CPU: 4 PID: 1039 Comm: qemu-system-x86 Tainted: G B 4.18.0-rc5+ #1 Hardware name: Supermicro Super Server/X10SRL-F, BIOS 2.0b 05/02/2017 Call Trace: dump_stack+0x5c/0x7b bad_page+0xba/0x120 get_page_from_freelist+0x1016/0x1250 __alloc_pages_nodemask+0xfa/0x250 alloc_pages_vma+0x7c/0x1c0 do_swap_page+0x347/0x920 ? __update_load_avg_se.isra.38+0x1eb/0x1f0 ? cpumask_next_wrap+0x3d/0x60 __handle_mm_fault+0x7b4/0x1110 ? update_load_avg+0x5ea/0x720 handle_mm_fault+0xfc/0x1f0 __get_user_pages+0x12f/0x690 get_user_pages_unlocked+0x148/0x1f0 __gfn_to_pfn_memslot+0xff/0x3c0 [kvm] try_async_pf+0x87/0x230 [kvm] tdp_page_fault+0x132/0x290 [kvm] ? vmexit_fill_RSB+0xc/0x30 [kvm_intel] kvm_mmu_page_fault+0x74/0x570 [kvm] ? vmexit_fill_RSB+0xc/0x30 [kvm_intel] ? vmexit_fill_RSB+0x18/0x30 [kvm_intel] ? vmexit_fill_RSB+0xc/0x30 [kvm_intel] ? vmexit_fill_RSB+0x18/0x30 [kvm_intel] ? vmexit_fill_RSB+0xc/0x30 [kvm_intel] ? vmexit_fill_RSB+0x18/0x30 [kvm_intel] ? vmexit_fill_RSB+0xc/0x30 [kvm_intel] ? vmexit_fill_RSB+0x18/0x30 [kvm_intel] ? vmexit_fill_RSB+0xc/0x30 [kvm_intel] ? vmexit_fill_RSB+0x18/0x30 [kvm_intel] ? vmexit_fill_RSB+0xc/0x30 [kvm_intel] ? vmx_vcpu_run+0x375/0x620 [kvm_intel] kvm_arch_vcpu_ioctl_run+0x9b3/0x1990 [kvm] ? __update_load_avg_se.isra.38+0x1eb/0x1f0 ? kvm_vcpu_ioctl+0x388/0x5d0 [kvm] kvm_vcpu_ioctl+0x388/0x5d0 [kvm] ? __switch_to+0x395/0x450 ? __switch_to+0x395/0x450 do_vfs_ioctl+0xa2/0x630 ? __schedule+0x3fd/0x890 ksys_ioctl+0x70/0x80 ? exit_to_usermode_loop+0xca/0xf0 __x64_sys_ioctl+0x16/0x20 do_syscall_64+0x55/0x100 entry_SYSCALL_64_after_hwframe+0x44/0xa9 RIP: 0033:0x7fb30361add7 Code: 00 00 00 48 8b 05 c1 80 2b 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 91 80 2b 00 f7 d8 64 89 01 48 RSP: 002b:00007fb2e97f98b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 000000000000ae80 RCX: 00007fb30361add7 RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000015 RBP: 00005652b984e0f0 R08: 00005652b7d513d0 R09: 0000000000000001 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007fb308c66000 R14: 0000000000000000 R15: 00005652b984e0f0 Link: https://lore.kernel.org/lkml/0516ae2d-b0fd-92c5-aa92-112ba7bd32fc@xxxxxxxxxx/ Reported-by: Tino Lehnig <tino.lehnig@xxxxxxxxxx> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx> Cc: Tino Lehnig <tino.lehnig@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> # v4.15+ Tested-by: Tino Lehnig <tino.lehnig@xxxxxxxxxx> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> --- drivers/block/zram/zram_drv.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 7436b2d27fa3..0b6eda1bd77a 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -298,7 +298,8 @@ static void reset_bdev(struct zram *zram) zram->backing_dev = NULL; zram->old_block_size = 0; zram->bdev = NULL; - + zram->disk->queue->backing_dev_info->capabilities |= + BDI_CAP_SYNCHRONOUS_IO; kvfree(zram->bitmap); zram->bitmap = NULL; } @@ -400,6 +401,8 @@ static ssize_t backing_dev_store(struct device *dev, zram->backing_dev = backing_dev; zram->bitmap = bitmap; zram->nr_pages = nr_pages; + zram->disk->queue->backing_dev_info->capabilities &= + ~BDI_CAP_SYNCHRONOUS_IO; up_write(&zram->init_lock); pr_info("setup backing device %s\n", file_name); -- 2.18.0.597.ga71716f1ad-goog
