summaryrefslogtreecommitdiffstats
path: root/fs/super.c
diff options
context:
space:
mode:
authorChristian Brauner <brauner@kernel.org>2023-08-23 13:06:55 +0200
committerChristian Brauner <brauner@kernel.org>2023-08-23 13:06:55 +0200
commit3fb5a6562adef115d8a8c3e19cc9d5fae32e93c8 (patch)
tree7a0cc61be2ba75aab26403f330da3140424b6b76 /fs/super.c
parentsuper: use higher-level helper for {freeze,thaw} (diff)
parentfs: wait for partially frozen filesystems (diff)
downloadlinux-3fb5a6562adef115d8a8c3e19cc9d5fae32e93c8.tar.xz
linux-3fb5a6562adef115d8a8c3e19cc9d5fae32e93c8.zip
Merge tag 'vfs-6.6-merge-2' of ssh://gitolite.kernel.org/pub/scm/fs/xfs/xfs-linux
Pull filesystem freezing updates from Darrick Wong: New code for 6.6: * Allow the kernel to initiate a freeze of a filesystem. The kernel and userspace can both hold a freeze on a filesystem at the same time; the freeze is not lifted until /both/ holders lift it. This will enable us to fix a longstanding bug in XFS online fsck. Signed-off-by: Darrick J. Wong <djwong@kernel.org> Message-Id: <20230822182604.GB11286@frogsfrogsfrogs> Signed-off-by: Christian Brauner <brauner@kernel.org>
Diffstat (limited to 'fs/super.c')
-rw-r--r--fs/super.c120
1 files changed, 102 insertions, 18 deletions
diff --git a/fs/super.c b/fs/super.c
index a284052ebab2..ef87103e2a51 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -39,7 +39,7 @@
#include <uapi/linux/mount.h>
#include "internal.h"
-static int thaw_super_locked(struct super_block *sb);
+static int thaw_super_locked(struct super_block *sb, enum freeze_holder who);
static LIST_HEAD(super_blocks);
static DEFINE_SPINLOCK(sb_lock);
@@ -1182,7 +1182,7 @@ static void do_thaw_all_callback(struct super_block *sb)
if (born && sb->s_root) {
emergency_thaw_bdev(sb);
- thaw_super_locked(sb);
+ thaw_super_locked(sb, FREEZE_HOLDER_USERSPACE);
} else {
super_unlock_excl(sb);
}
@@ -1836,14 +1836,43 @@ static void sb_freeze_unlock(struct super_block *sb, int level)
percpu_up_write(sb->s_writers.rw_sem + level);
}
+static int wait_for_partially_frozen(struct super_block *sb)
+{
+ int ret = 0;
+
+ do {
+ unsigned short old = sb->s_writers.frozen;
+
+ up_write(&sb->s_umount);
+ ret = wait_var_event_killable(&sb->s_writers.frozen,
+ sb->s_writers.frozen != old);
+ down_write(&sb->s_umount);
+ } while (ret == 0 &&
+ sb->s_writers.frozen != SB_UNFROZEN &&
+ sb->s_writers.frozen != SB_FREEZE_COMPLETE);
+
+ return ret;
+}
+
/**
* freeze_super - lock the filesystem and force it into a consistent state
* @sb: the super to lock
+ * @who: context that wants to freeze
*
* Syncs the super to make sure the filesystem is consistent and calls the fs's
- * freeze_fs. Subsequent calls to this without first thawing the fs will return
+ * freeze_fs. Subsequent calls to this without first thawing the fs may return
* -EBUSY.
*
+ * @who should be:
+ * * %FREEZE_HOLDER_USERSPACE if userspace wants to freeze the fs;
+ * * %FREEZE_HOLDER_KERNEL if the kernel wants to freeze the fs.
+ *
+ * The @who argument distinguishes between the kernel and userspace trying to
+ * freeze the filesystem. Although there cannot be multiple kernel freezes or
+ * multiple userspace freezes in effect at any given time, the kernel and
+ * userspace can both hold a filesystem frozen. The filesystem remains frozen
+ * until there are no kernel or userspace freezes in effect.
+ *
* During this function, sb->s_writers.frozen goes through these values:
*
* SB_UNFROZEN: File system is normal, all writes progress as usual.
@@ -1869,20 +1898,40 @@ static void sb_freeze_unlock(struct super_block *sb, int level)
*
* sb->s_writers.frozen is protected by sb->s_umount.
*/
-int freeze_super(struct super_block *sb)
+int freeze_super(struct super_block *sb, enum freeze_holder who)
{
int ret;
- /* Since the caller must already have an active reference... */
atomic_inc(&sb->s_active);
-
- /* ...@sb definitely can't be dying. */
if (!super_lock_excl(sb))
WARN(1, "Dying superblock while freezing!");
+retry:
+ if (sb->s_writers.frozen == SB_FREEZE_COMPLETE) {
+ if (sb->s_writers.freeze_holders & who) {
+ deactivate_locked_super(sb);
+ return -EBUSY;
+ }
+
+ WARN_ON(sb->s_writers.freeze_holders == 0);
+
+ /*
+ * Someone else already holds this type of freeze; share the
+ * freeze and assign the active ref to the freeze.
+ */
+ sb->s_writers.freeze_holders |= who;
+ super_unlock_excl(sb);
+ return 0;
+ }
+
if (sb->s_writers.frozen != SB_UNFROZEN) {
- deactivate_locked_super(sb);
- return -EBUSY;
+ ret = wait_for_partially_frozen(sb);
+ if (ret) {
+ deactivate_locked_super(sb);
+ return ret;
+ }
+
+ goto retry;
}
if (!(sb->s_flags & SB_BORN)) {
@@ -1892,7 +1941,9 @@ int freeze_super(struct super_block *sb)
if (sb_rdonly(sb)) {
/* Nothing to do really... */
+ sb->s_writers.freeze_holders |= who;
sb->s_writers.frozen = SB_FREEZE_COMPLETE;
+ wake_up_var(&sb->s_writers.frozen);
super_unlock_excl(sb);
return 0;
}
@@ -1901,8 +1952,6 @@ int freeze_super(struct super_block *sb)
/* Release s_umount to preserve sb_start_write -> s_umount ordering */
super_unlock_excl(sb);
sb_wait_write(sb, SB_FREEZE_WRITE);
-
- /* We're still holding an active reference. */
if (!super_lock_excl(sb))
WARN(1, "Dying superblock while freezing!");
@@ -1915,6 +1964,7 @@ int freeze_super(struct super_block *sb)
if (ret) {
sb->s_writers.frozen = SB_UNFROZEN;
sb_freeze_unlock(sb, SB_FREEZE_PAGEFAULT);
+ wake_up_var(&sb->s_writers.frozen);
deactivate_locked_super(sb);
return ret;
}
@@ -1930,6 +1980,7 @@ int freeze_super(struct super_block *sb)
"VFS:Filesystem freeze failed\n");
sb->s_writers.frozen = SB_UNFROZEN;
sb_freeze_unlock(sb, SB_FREEZE_FS);
+ wake_up_var(&sb->s_writers.frozen);
deactivate_locked_super(sb);
return ret;
}
@@ -1938,24 +1989,50 @@ int freeze_super(struct super_block *sb)
* For debugging purposes so that fs can warn if it sees write activity
* when frozen is set to SB_FREEZE_COMPLETE, and for thaw_super().
*/
+ sb->s_writers.freeze_holders |= who;
sb->s_writers.frozen = SB_FREEZE_COMPLETE;
+ wake_up_var(&sb->s_writers.frozen);
lockdep_sb_freeze_release(sb);
super_unlock_excl(sb);
return 0;
}
EXPORT_SYMBOL(freeze_super);
-static int thaw_super_locked(struct super_block *sb)
+/*
+ * Undoes the effect of a freeze_super_locked call. If the filesystem is
+ * frozen both by userspace and the kernel, a thaw call from either source
+ * removes that state without releasing the other state or unlocking the
+ * filesystem.
+ */
+static int thaw_super_locked(struct super_block *sb, enum freeze_holder who)
{
int error;
- if (sb->s_writers.frozen != SB_FREEZE_COMPLETE) {
+ if (sb->s_writers.frozen == SB_FREEZE_COMPLETE) {
+ if (!(sb->s_writers.freeze_holders & who)) {
+ super_unlock_excl(sb);
+ return -EINVAL;
+ }
+
+ /*
+ * Freeze is shared with someone else. Release our hold and
+ * drop the active ref that freeze_super assigned to the
+ * freezer.
+ */
+ if (sb->s_writers.freeze_holders & ~who) {
+ sb->s_writers.freeze_holders &= ~who;
+ deactivate_locked_super(sb);
+ return 0;
+ }
+ } else {
super_unlock_excl(sb);
return -EINVAL;
}
if (sb_rdonly(sb)) {
+ sb->s_writers.freeze_holders &= ~who;
sb->s_writers.frozen = SB_UNFROZEN;
+ wake_up_var(&sb->s_writers.frozen);
goto out;
}
@@ -1964,15 +2041,16 @@ static int thaw_super_locked(struct super_block *sb)
if (sb->s_op->unfreeze_fs) {
error = sb->s_op->unfreeze_fs(sb);
if (error) {
- printk(KERN_ERR
- "VFS:Filesystem thaw failed\n");
+ printk(KERN_ERR "VFS:Filesystem thaw failed\n");
lockdep_sb_freeze_release(sb);
super_unlock_excl(sb);
return error;
}
}
+ sb->s_writers.freeze_holders &= ~who;
sb->s_writers.frozen = SB_UNFROZEN;
+ wake_up_var(&sb->s_writers.frozen);
sb_freeze_unlock(sb, SB_FREEZE_FS);
out:
deactivate_locked_super(sb);
@@ -1982,14 +2060,20 @@ out:
/**
* thaw_super -- unlock filesystem
* @sb: the super to thaw
+ * @who: context that wants to freeze
+ *
+ * Unlocks the filesystem and marks it writeable again after freeze_super()
+ * if there are no remaining freezes on the filesystem.
*
- * Unlocks the filesystem and marks it writeable again after freeze_super().
+ * @who should be:
+ * * %FREEZE_HOLDER_USERSPACE if userspace wants to thaw the fs;
+ * * %FREEZE_HOLDER_KERNEL if the kernel wants to thaw the fs.
*/
-int thaw_super(struct super_block *sb)
+int thaw_super(struct super_block *sb, enum freeze_holder who)
{
if (!super_lock_excl(sb))
WARN(1, "Dying superblock while thawing!");
- return thaw_super_locked(sb);
+ return thaw_super_locked(sb, who);
}
EXPORT_SYMBOL(thaw_super);