From b43a9e76b4cc78cdaa8c809dd31cd452797b7661 Mon Sep 17 00:00:00 2001 From: Roman Gushchin Date: Fri, 23 Jul 2021 15:50:29 -0700 Subject: writeback, cgroup: remove wb from offline list before releasing refcnt Boyang reported that the commit c22d70a162d3 ("writeback, cgroup: release dying cgwbs by switching attached inodes") causes the kernel to crash while running xfstests generic/256 on ext4 on aarch64 and ppc64le. run fstests generic/256 at 2021-07-12 05:41:40 EXT4-fs (vda3): mounted filesystem with ordered data mode. Opts: . Quota mode: none. Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 Mem abort info: ESR = 0x96000005 EC = 0x25: DABT (current EL), IL = 32 bits SET = 0, FnV = 0 EA = 0, S1PTW = 0 FSC = 0x05: level 1 translation fault Data abort info: ISV = 0, ISS = 0x00000005 CM = 0, WnR = 0 user pgtable: 64k pages, 48-bit VAs, pgdp=00000000b0502000 [0000000000000000] pgd=0000000000000000, p4d=0000000000000000, pud=0000000000000000 Internal error: Oops: 96000005 [#1] SMP Modules linked in: dm_flakey dm_snapshot dm_bufio dm_zero dm_mod loop tls rpcsec_gss_krb5 auth_rpcgss nfsv4 dns_resolver nfs lockd grace fscache netfs rfkill sunrpc ext4 vfat fat mbcache jbd2 drm fuse xfs libcrc32c crct10dif_ce ghash_ce sha2_ce sha256_arm64 sha1_ce virtio_blk virtio_net net_failover virtio_console failover virtio_mmio aes_neon_bs [last unloaded: scsi_debug] CPU: 0 PID: 408468 Comm: kworker/u8:5 Tainted: G X --------- --- 5.14.0-0.rc1.15.bx.el9.aarch64 #1 Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015 Workqueue: events_unbound cleanup_offline_cgwbs_workfn pstate: 004000c5 (nzcv daIF +PAN -UAO -TCO BTYPE=--) pc : cleanup_offline_cgwbs_workfn+0x320/0x394 lr : cleanup_offline_cgwbs_workfn+0xe0/0x394 sp : ffff80001554fd10 x29: ffff80001554fd10 x28: 0000000000000000 x27: 0000000000000001 x26: 0000000000000000 x25: 00000000000000e0 x24: ffffd2a2fbe671a8 x23: ffff80001554fd88 x22: ffffd2a2fbe67198 x21: ffffd2a2fc25a730 x20: ffff210412bc3000 x19: ffff210412bc3280 x18: 0000000000000000 x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 x14: 0000000000000000 x13: 0000000000000030 x12: 0000000000000040 x11: ffff210481572238 x10: ffff21048157223a x9 : ffffd2a2fa276c60 x8 : ffff210484106b60 x7 : 0000000000000000 x6 : 000000000007d18a x5 : ffff210416a86400 x4 : ffff210412bc0280 x3 : 0000000000000000 x2 : ffff80001554fd88 x1 : ffff210412bc0280 x0 : 0000000000000003 Call trace: cleanup_offline_cgwbs_workfn+0x320/0x394 process_one_work+0x1f4/0x4b0 worker_thread+0x184/0x540 kthread+0x114/0x120 ret_from_fork+0x10/0x18 Code: d63f0020 97f99963 17ffffa6 f8588263 (f9400061) ---[ end trace e250fe289272792a ]--- Kernel panic - not syncing: Oops: Fatal exception SMP: stopping secondary CPUs SMP: failed to stop secondary CPUs 0-2 Kernel Offset: 0x52a2e9fa0000 from 0xffff800010000000 PHYS_OFFSET: 0xfff0defca0000000 CPU features: 0x00200251,23200840 Memory Limit: none ---[ end Kernel panic - not syncing: Oops: Fatal exception ]--- The problem happens when cgwb_release_workfn() races with cleanup_offline_cgwbs_workfn(): wb_tryget() in cleanup_offline_cgwbs_workfn() can be called after percpu_ref_exit() is cgwb_release_workfn(), which is basically a use-after-free error. Fix the problem by making removing the writeback structure from the offline list before releasing the percpu reference counter. It will guarantee that cleanup_offline_cgwbs_workfn() will not see and not access writeback structures which are about to be released. Link: https://lkml.kernel.org/r/20210716201039.3762203-1-guro@fb.com Fixes: c22d70a162d3 ("writeback, cgroup: release dying cgwbs by switching attached inodes") Signed-off-by: Roman Gushchin Reported-by: Boyang Xue Suggested-by: Jan Kara Tested-by: Darrick J. Wong Cc: Will Deacon Cc: Dave Chinner Cc: Murphy Zhou Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/backing-dev.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'mm') diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 271f2ca862c8..f5561ea7d90a 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -398,12 +398,12 @@ static void cgwb_release_workfn(struct work_struct *work) blkcg_unpin_online(blkcg); fprop_local_destroy_percpu(&wb->memcg_completions); - percpu_ref_exit(&wb->refcnt); spin_lock_irq(&cgwb_lock); list_del(&wb->offline_node); spin_unlock_irq(&cgwb_lock); + percpu_ref_exit(&wb->refcnt); wb_exit(wb); WARN_ON_ONCE(!list_empty(&wb->b_attached)); kfree_rcu(wb, rcu); -- cgit v1.2.3