On Fri, May 11, 2018 at 12:09:42PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> Similar to log_recovery_delay, this delay occurs between the VFS
> superblock being initialised and the xfs_mount being fully
> initialised. It also poisons the per-ag radix tree node so that it
> can be used for triggering shrinker races during mount
> such as the following:
>
> <run memory pressure workload in background>
>
> $ cat dirty-mount.sh
> #! /bin/bash
>
> umount -f /dev/pmem0
> mkfs.xfs -f /dev/pmem0
> mount /dev/pmem0 /mnt/test
> rm -f /mnt/test/foo
> xfs_io -fxc "pwrite 0 4k" -c fsync -c "shutdown" /mnt/test/foo
> umount /dev/pmem0
>
> # let's crash it now!
> echo 30 > /sys/fs/xfs/debug/mount_delay
> mount /dev/pmem0 /mnt/test
> echo 0 > /sys/fs/xfs/debug/mount_delay
> umount /dev/pmem0
> $ sudo ./dirty-mount.sh
> .....
> [ 60.378118] CPU: 3 PID: 3577 Comm: fs_mark Tainted: G D W 4.16.0-rc5-dgc #440
> [ 60.378120] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> [ 60.378124] RIP: 0010:radix_tree_next_chunk+0x76/0x320
> [ 60.378127] RSP: 0018:ffffc9000276f4f8 EFLAGS: 00010282
> [ 60.383670] RAX: a5a5a5a5a5a5a5a4 RBX: 0000000000000010 RCX: 000000000000001a
> [ 60.385277] RDX: 0000000000000000 RSI: ffffc9000276f540 RDI: 0000000000000000
> [ 60.386554] RBP: 0000000000000000 R08: 0000000000000000 R09: a5a5a5a5a5a5a5a5
> [ 60.388194] R10: 0000000000000006 R11: 0000000000000001 R12: ffffc9000276f598
> [ 60.389288] R13: 0000000000000040 R14: 0000000000000228 R15: ffff880816cd6458
> [ 60.390827] FS: 00007f5c124b9740(0000) GS:ffff88083fc00000(0000) knlGS:0000000000000000
> [ 60.392253] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 60.393423] CR2: 00007f5c11bba0b8 CR3: 000000035580e001 CR4: 00000000000606e0
> [ 60.394519] Call Trace:
> [ 60.395252] radix_tree_gang_lookup_tag+0xc4/0x130
> [ 60.395948] xfs_perag_get_tag+0x37/0xf0
> [ 60.396522] xfs_reclaim_inodes_count+0x32/0x40
> [ 60.397178] xfs_fs_nr_cached_objects+0x11/0x20
> [ 60.397837] super_cache_count+0x35/0xc0
> [ 60.399159] shrink_slab.part.66+0xb1/0x370
> [ 60.400194] shrink_node+0x7e/0x1a0
> [ 60.401058] try_to_free_pages+0x199/0x470
> [ 60.402081] __alloc_pages_slowpath+0x3a1/0xd20
> [ 60.403729] __alloc_pages_nodemask+0x1c3/0x200
> [ 60.404941] cache_grow_begin+0x20b/0x2e0
> [ 60.406164] fallback_alloc+0x160/0x200
> [ 60.407088] kmem_cache_alloc+0x111/0x4e0
> [ 60.408038] ? xfs_buf_rele+0x61/0x430
> [ 60.408925] kmem_zone_alloc+0x61/0xe0
> [ 60.409965] xfs_inode_alloc+0x24/0x1d0
> .....
>
>
> Signed-Off-By: Dave Chinner <dchinner@xxxxxxxxxx>
> Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
Looks ok, will test...
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
--D
> ---
> fs/xfs/xfs_globals.c | 1 +
> fs/xfs/xfs_super.c | 11 +++++++++++
> fs/xfs/xfs_sysctl.h | 1 +
> fs/xfs/xfs_sysfs.c | 31 +++++++++++++++++++++++++++++++
> 4 files changed, 44 insertions(+)
>
> diff --git a/fs/xfs/xfs_globals.c b/fs/xfs/xfs_globals.c
> index 3e1cc3001bcb..fdde17a2333c 100644
> --- a/fs/xfs/xfs_globals.c
> +++ b/fs/xfs/xfs_globals.c
> @@ -47,6 +47,7 @@ xfs_param_t xfs_params = {
>
> struct xfs_globals xfs_globals = {
> .log_recovery_delay = 0, /* no delay by default */
> + .mount_delay = 0, /* no delay by default */
> #ifdef XFS_ASSERT_FATAL
> .bug_on_assert = true, /* assert failures BUG() */
> #else
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 5726ef496980..a523eaeb3f29 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -1635,6 +1635,17 @@ xfs_fs_fill_super(
> #endif
> sb->s_op = &xfs_super_operations;
>
> + /*
> + * Delay mount work if the debug hook is set. This is debug
> + * instrumention to coordinate simulation of xfs mount failures with
> + * VFS superblock operations
> + */
> + if (xfs_globals.mount_delay) {
> + xfs_notice(mp, "Delaying mount for %d seconds.",
> + xfs_globals.mount_delay);
> + msleep(xfs_globals.mount_delay * 1000);
> + }
> +
> if (silent)
> flags |= XFS_MFSI_QUIET;
>
> diff --git a/fs/xfs/xfs_sysctl.h b/fs/xfs/xfs_sysctl.h
> index 82afee005140..b53a33e69932 100644
> --- a/fs/xfs/xfs_sysctl.h
> +++ b/fs/xfs/xfs_sysctl.h
> @@ -95,6 +95,7 @@ extern xfs_param_t xfs_params;
>
> struct xfs_globals {
> int log_recovery_delay; /* log recovery delay (secs) */
> + int mount_delay; /* mount setup delay (secs) */
> bool bug_on_assert; /* BUG() the kernel on assert failure */
> };
> extern struct xfs_globals xfs_globals;
> diff --git a/fs/xfs/xfs_sysfs.c b/fs/xfs/xfs_sysfs.c
> index 8b2ccc234f36..2d5cd2529f8e 100644
> --- a/fs/xfs/xfs_sysfs.c
> +++ b/fs/xfs/xfs_sysfs.c
> @@ -165,9 +165,40 @@ log_recovery_delay_show(
> }
> XFS_SYSFS_ATTR_RW(log_recovery_delay);
>
> +STATIC ssize_t
> +mount_delay_store(
> + struct kobject *kobject,
> + const char *buf,
> + size_t count)
> +{
> + int ret;
> + int val;
> +
> + ret = kstrtoint(buf, 0, &val);
> + if (ret)
> + return ret;
> +
> + if (val < 0 || val > 60)
> + return -EINVAL;
> +
> + xfs_globals.mount_delay = val;
> +
> + return count;
> +}
> +
> +STATIC ssize_t
> +mount_delay_show(
> + struct kobject *kobject,
> + char *buf)
> +{
> + return snprintf(buf, PAGE_SIZE, "%d\n", xfs_globals.mount_delay);
> +}
> +XFS_SYSFS_ATTR_RW(mount_delay);
> +
> static struct attribute *xfs_dbg_attrs[] = {
> ATTR_LIST(bug_on_assert),
> ATTR_LIST(log_recovery_delay),
> + ATTR_LIST(mount_delay),
> NULL,
> };
>
> --
> 2.17.0
>
> --
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