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>
---
fs/xfs/xfs_globals.c | 1 +
fs/xfs/xfs_super.c | 12 ++++++++++++
fs/xfs/xfs_sysctl.h | 1 +
fs/xfs/xfs_sysfs.c | 31 +++++++++++++++++++++++++++++++
4 files changed, 45 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 4944fe37fc95..ee26437dc567 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1617,6 +1617,18 @@ 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) {
+ memset(&mp->m_perag_tree, 0xa5, sizeof(mp->m_perag_tree));
+ 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,
};
--
2.16.1
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