linux/mm/backing-dev.c, branch v5.14

writeback, cgroup: remove wb from offline list before releasing refcnt

2021-07-24T00:43:28Z

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

writeback, cgroup: release dying cgwbs by switching attached inodes

2021-06-29T17:53:48Z

Asynchronously try to release dying cgwbs by switching attached inodes to the nearest living ancestor wb. It helps to get rid of per-cgroup writeback structures themselves and of pinned memory and block cgroups, which are significantly larger structures (mostly due to large per-cpu statistics data). This prevents memory waste and helps to avoid different scalability problems caused by large piles of dying cgroups. Reuse the existing mechanism of inode switching used for foreign inode detection. To speed things up batch up to 115 inode switching in a single operation (the maximum number is selected so that the resulting struct inode_switch_wbs_context can fit into 1024 bytes). Because every switching consists of two steps divided by an RCU grace period, it would be too slow without batching. Please note that the whole batch counts as a single operation (when increasing/decreasing isw_nr_in_flight). This allows to keep umounting working (flush the switching queue), however prevents cleanups from consuming the whole switching quota and effectively blocking the frn switching. A cgwb cleanup operation can fail due to different reasons (e.g. not enough memory, the cgwb has an in-flight/pending io, an attached inode in a wrong state, etc). In this case the next scheduled cleanup will make a new attempt. An attempt is made each time a new cgwb is offlined (in other words a memcg and/or a blkcg is deleted by a user). In the future an additional attempt scheduled by a timer can be implemented. [guro@fb.com: replace open-coded "115" with arithmetic] Link: https://lkml.kernel.org/r/YMEcSBcq/VXMiPPO@carbon.dhcp.thefacebook.com [guro@fb.com: add smp_mb() to inode_prepare_wbs_switch()] Link: https://lkml.kernel.org/r/YMFa+guFw7OFjf3X@carbon.dhcp.thefacebook.com [willy@infradead.org: fix documentation] Link: https://lkml.kernel.org/r/20210615200242.1716568-2-willy@infradead.org Link: https://lkml.kernel.org/r/20210608230225.2078447-9-guro@fb.com Signed-off-by: Roman Gushchin Signed-off-by: Matthew Wilcox (Oracle) Acked-by: Tejun Heo Acked-by: Dennis Zhou Reviewed-by: Jan Kara Cc: Alexander Viro Cc: Dave Chinner Cc: Jan Kara Cc: Jens Axboe Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

writeback, cgroup: keep list of inodes attached to bdi_writeback

2021-06-29T17:53:48Z

Currently there is no way to iterate over inodes attached to a specific cgwb structure. It limits the ability to efficiently reclaim the writeback structure itself and associated memory and block cgroup structures without scanning all inodes belonging to a sb, which can be prohibitively expensive. While dirty/in-active-writeback an inode belongs to one of the bdi_writeback's io lists: b_dirty, b_io, b_more_io and b_dirty_time. Once cleaned up, it's removed from all io lists. So the inode->i_io_list can be reused to maintain the list of inodes, attached to a bdi_writeback structure. This patch introduces a new wb->b_attached list, which contains all inodes which were dirty at least once and are attached to the given cgwb. Inodes attached to the root bdi_writeback structures are never placed on such list. The following patch will use this list to try to release cgwbs structures more efficiently. Link: https://lkml.kernel.org/r/20210608230225.2078447-6-guro@fb.com Signed-off-by: Roman Gushchin Suggested-by: Jan Kara Reviewed-by: Jan Kara Acked-by: Tejun Heo Acked-by: Dennis Zhou Cc: Alexander Viro Cc: Dave Chinner Cc: Jan Kara Cc: Jens Axboe Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/backing-dev.c: use might_alloc()

2021-02-26T17:41:01Z

Now that my little helper has landed, use it more. On top of the existing check this also uses lockdep through the fs_reclaim annotations. [akpm@linux-foundation.org: include linux/sched/mm.h] Link: https://lkml.kernel.org/r/20210113135009.3606813-2-daniel.vetter@ffwll.ch Signed-off-by: Daniel Vetter Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: backing-dev: Remove duplicated macro definition

2021-02-24T21:38:28Z

Move the K() macro a little forward to remove the same macro definition. Link: https://lkml.kernel.org/r/d1ccdf2d3116dce9814f2bcc1f0415ecb4c76ea5.1612862230.git.baolin.wang@linux.alibaba.com Signed-off-by: Baolin Wang Reviewed-by: Andrew Morton Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm:backing-dev: use sysfs_emit in macro defining functions

2020-12-15T20:13:47Z

The cocci script used in commit bdacbb8d04f ("mm: Use sysfs_emit for struct kobject * uses") does not convert the name##_show macro because the macro uses concatenation via ##. Convert it by hand. Link: https://lkml.kernel.org/r/45ec6cfc177d743f9c0ebaf35e43969dce43af42.1605376435.git.joe@perches.com Signed-off-by: Joe Perches Cc: Christoph Lameter Cc: David Rientjes Cc: Greg Kroah-Hartman Cc: Hugh Dickins Cc: Joonsoo Kim Cc: Matthew Wilcox Cc: Mike Kravetz Cc: Pekka Enberg Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

bdi: replace BDI_CAP_NO_{WRITEBACK,ACCT_DIRTY} with a single flag

2020-09-24T19:43:39Z

Replace the two negative flags that are always used together with a single positive flag that indicates the writeback capability instead of two related non-capabilities. Also remove the pointless wrappers to just check the flag. Signed-off-by: Christoph Hellwig Reviewed-by: Jan Kara Reviewed-by: Johannes Thumshirn Signed-off-by: Jens Axboe

bdi: invert BDI_CAP_NO_ACCT_WB

2020-09-24T19:43:39Z

Replace BDI_CAP_NO_ACCT_WB with a positive BDI_CAP_WRITEBACK_ACCT to make the checks more obvious. Also remove the pointless bdi_cap_account_writeback wrapper that just obsfucates the check. Signed-off-by: Christoph Hellwig Reviewed-by: Jan Kara Reviewed-by: Johannes Thumshirn Signed-off-by: Jens Axboe

bdi: replace BDI_CAP_STABLE_WRITES with a queue and a sb flag

2020-09-24T19:43:39Z

The BDI_CAP_STABLE_WRITES is one of the few bits of information in the backing_dev_info shared between the block drivers and the writeback code. To help untangling the dependency replace it with a queue flag and a superblock flag derived from it. This also helps with the case of e.g. a file system requiring stable writes due to its own checksumming, but not forcing it on other users of the block device like the swap code. One downside is that we an't support the stable_pages_required bdi attribute in sysfs anymore. It is replaced with a queue attribute which also is writable for easier testing. Signed-off-by: Christoph Hellwig Reviewed-by: Jan Kara Reviewed-by: Johannes Thumshirn Signed-off-by: Jens Axboe

bdi: initialize ->ra_pages and ->io_pages in bdi_init

2020-09-24T19:43:39Z

Set up a readahead size by default, as very few users have a good reason to change it. This means code, ecryptfs, and orangefs now set up the values while they were previously missing it, while ubifs, mtd and vboxsf manually set it to 0 to avoid readahead. Signed-off-by: Christoph Hellwig Reviewed-by: Jan Kara Acked-by: David Sterba [btrfs] Acked-by: Richard Weinberger [ubifs, mtd] Signed-off-by: Jens Axboe