At 03/30/2017 08:34 AM, Liu Bo wrote:
On Wed, Mar 29, 2017 at 09:33:18AM +0800, Qu Wenruo wrote:
Unlike mirror based profiles, RAID5/6 recovery needs to read out the
whole full stripe.
And if we don't do proper protect, it can easily cause race condition.
Introduce 2 new functions: lock_full_stripe() and unlock_full_stripe()
for RAID5/6.
Which stores a rb_tree of mutex for full stripes, so scrub callers can
use them to lock a full stripe to avoid race.
Signed-off-by: Qu Wenruo <quwenruo@xxxxxxxxxxxxxx>
---
fs/btrfs/ctree.h | 17 ++++
fs/btrfs/extent-tree.c | 2 +
fs/btrfs/scrub.c | 212 +++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 231 insertions(+)
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 29b7fc28c607..9fe56da21fed 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -538,6 +538,14 @@ struct btrfs_io_ctl {
unsigned check_crcs:1;
};
+/*
+ * Tree to record all locked full stripes of a RAID5/6 block group
+ */
+struct btrfs_full_stripe_locks_tree {
+ struct rb_root root;
+ struct mutex lock;
+};
+
struct btrfs_block_group_cache {
struct btrfs_key key;
struct btrfs_block_group_item item;
@@ -648,6 +656,9 @@ struct btrfs_block_group_cache {
* Protected by free_space_lock.
*/
int needs_free_space;
+
+ /* Record locked full stripes for RAID5/6 block group */
+ struct btrfs_full_stripe_locks_tree full_stripe_locks_root;
};
/* delayed seq elem */
@@ -3647,6 +3658,12 @@ int btrfs_scrub_cancel_dev(struct btrfs_fs_info *info,
struct btrfs_device *dev);
int btrfs_scrub_progress(struct btrfs_fs_info *fs_info, u64 devid,
struct btrfs_scrub_progress *progress);
+static inline void btrfs_init_full_stripe_locks_tree(
+ struct btrfs_full_stripe_locks_tree *locks_root)
+{
+ locks_root->root = RB_ROOT;
+ mutex_init(&locks_root->lock);
+}
/* dev-replace.c */
void btrfs_bio_counter_inc_blocked(struct btrfs_fs_info *fs_info);
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index be5477676cc8..e4d48997d927 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -131,6 +131,7 @@ void btrfs_put_block_group(struct btrfs_block_group_cache *cache)
if (atomic_dec_and_test(&cache->count)) {
WARN_ON(cache->pinned > 0);
WARN_ON(cache->reserved > 0);
+ WARN_ON(!RB_EMPTY_ROOT(&cache->full_stripe_locks_root.root));
It's also necessary to free objects left in the rbtree because we may get here
due to -ENOMEM in unlock_full_stripe.c
Nope, unlock_full_stripe() won't return -ENOMEM.
So here, if full_stripe_locks_root are not empty, it means that some one
inserted a full stripe lock but doesn't even unlock it.
In that case, they still hold the mutex, and we can't really help but
warn and continue since only the lock holder could release the mutex.
kfree(cache->free_space_ctl);
kfree(cache);
}
@@ -9917,6 +9918,7 @@ btrfs_create_block_group_cache(struct btrfs_fs_info *fs_info,
btrfs_init_free_space_ctl(cache);
atomic_set(&cache->trimming, 0);
mutex_init(&cache->free_space_lock);
+ btrfs_init_full_stripe_locks_tree(&cache->full_stripe_locks_root);
return cache;
}
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index b0251eb1239f..ab33b9a8aac2 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -240,6 +240,13 @@ struct scrub_warning {
struct btrfs_device *dev;
};
+struct full_stripe_lock {
+ struct rb_node node;
+ u64 logical;
+ u64 refs;
+ struct mutex mutex;
+};
+
static void scrub_pending_bio_inc(struct scrub_ctx *sctx);
static void scrub_pending_bio_dec(struct scrub_ctx *sctx);
static void scrub_pending_trans_workers_inc(struct scrub_ctx *sctx);
@@ -349,6 +356,211 @@ static void scrub_blocked_if_needed(struct btrfs_fs_info *fs_info)
}
/*
+ * Insert new full stripe lock into full stripe locks tree
+ *
+ * Return pointer to existing or newly inserted full_stripe_lock structure if
+ * everything works well.
+ * Return ERR_PTR(-ENOMEM) if we failed to allocate memory
+ *
+ * NOTE: caller must hold full_stripe_locks_root->lock before calling this
+ * function
+ */
+static struct full_stripe_lock *insert_full_stripe_lock(
+ struct btrfs_full_stripe_locks_tree *locks_root,
+ u64 fstripe_logical)
+{
+ struct rb_node **p;
+ struct rb_node *parent = NULL;
+ struct full_stripe_lock *entry;
+ struct full_stripe_lock *ret;
+
+ WARN_ON(!mutex_is_locked(&locks_root->lock));
+
+ p = &locks_root->root.rb_node;
+ while (*p) {
+ parent = *p;
+ entry = rb_entry(parent, struct full_stripe_lock, node);
+ if (fstripe_logical < entry->logical) {
+ p = &(*p)->rb_left;
+ } else if (fstripe_logical > entry->logical) {
+ p = &(*p)->rb_right;
+ } else {
+ entry->refs++;
+ return entry;
+ }
+ }
+
+ /* Insert new lock */
+ ret = kmalloc(sizeof(*ret), GFP_KERNEL);
+ if (!ret)
+ return ERR_PTR(-ENOMEM);
+ ret->logical = fstripe_logical;
+ ret->refs = 1;
+ mutex_init(&ret->mutex);
+
+ rb_link_node(&ret->node, parent, p);
+ rb_insert_color(&ret->node, &locks_root->root);
+ return ret;
+}
+
+/*
+ * Search for a full stripe lock of a block group
+ *
+ * Return pointer to existing full stripe lock if found
+ * Return NULL if not found
+ */
+static struct full_stripe_lock *search_full_stripe_lock(
+ struct btrfs_full_stripe_locks_tree *locks_root,
+ u64 fstripe_logical)
+{
+ struct rb_node *node;
+ struct full_stripe_lock *entry;
+
+ WARN_ON(!mutex_is_locked(&locks_root->lock));
+
+ node = locks_root->root.rb_node;
+ while (node) {
+ entry = rb_entry(node, struct full_stripe_lock, node);
+ if (fstripe_logical < entry->logical)
+ node = node->rb_left;
+ else if (fstripe_logical > entry->logical)
+ node = node->rb_right;
+ else
+ return entry;
+ }
+ return NULL;
+}
+
+/*
+ * Helper to get full stripe logical from a normal bytenr.
+ * Thanks to the chaos of scrub structures, we need to get it all
+ * by ourselves, using btrfs_map_sblock().
+ */
+static int get_full_stripe_logical(struct btrfs_fs_info *fs_info, u64 bytenr,
+ u64 *bytenr_ret)
+{
+ struct btrfs_bio *bbio = NULL;
+ u64 len;
+ int ret;
+
+ /* Just use map_sblock() to get full stripe logical */
+ ret = btrfs_map_sblock(fs_info, BTRFS_MAP_GET_READ_MIRRORS, bytenr,
+ &len, &bbio, 0, 1);
+ if (ret || !bbio || !bbio->raid_map)
+ goto error;
+ *bytenr_ret = bbio->raid_map[0];
If only the start logical address of a full stripe is needed, we could
get it by aligning
(bytenr - block_group_start) to (nr_data_stripes * stripe_len).
Good idea, and this avoids the possible error returned from map_sblock().
+ btrfs_put_bbio(bbio);
+ return 0;
+error:
+ btrfs_put_bbio(bbio);
+ if (ret)
+ return ret;
+ return -EIO;
+}
+
+/*
+ * To lock a full stripe to avoid concurrency of recovery and read
+ * It's only used for profiles with parities(RAID5/6), for other profiles it
+ * does nothing
+ *
+ * Return 0 if we locked full stripe covering @bytenr, with a mutex hold.
+ * So caller must call unlock_full_stripe() at the same context.
+ *
+ * Return <0 if encounters error.
+ */
+static int lock_full_stripe(struct btrfs_fs_info *fs_info, u64 bytenr)
+{
+ struct btrfs_block_group_cache *bg_cache;
+ struct btrfs_full_stripe_locks_tree *locks_root;
+ struct full_stripe_lock *existing;
+ u64 fstripe_start;
+ int ret = 0;
+
+ bg_cache = btrfs_lookup_block_group(fs_info, bytenr);
+ if (!bg_cache)
+ return -ENOENT;
+
When starting to scrub a chunk, we've already increased a ref for block group,
could you please put a ASSERT to catch it?
Personally I prefer WARN_ON() than ASSERT().
ASSERT() always panic the modules and forces us to reset the system.
Wiping out any possibility to check the system.
+ /* Profiles not based on parity don't need full stripe lock */
+ if (!(bg_cache->flags & BTRFS_BLOCK_GROUP_RAID56_MASK))
+ goto out;
+ locks_root = &bg_cache->full_stripe_locks_root;
+
+ ret = get_full_stripe_logical(fs_info, bytenr, &fstripe_start);
+ if (ret < 0)
+ goto out;
+
+ /* Now insert the full stripe lock */
+ mutex_lock(&locks_root->lock);
+ existing = insert_full_stripe_lock(locks_root, fstripe_start);
+ mutex_unlock(&locks_root->lock);
+ if (IS_ERR(existing)) {
+ ret = PTR_ERR(existing);
+ goto out;
+ }
+ mutex_lock(&existing->mutex);
+out:
+ btrfs_put_block_group(bg_cache);
+ return ret;
+}
+
+/*
+ * Unlock a full stripe.
+ * NOTE: Caller must ensure it's the same context calling corresponding
+ * lock_full_stripe().
+ *
+ * Return 0 if we unlock full stripe without problem.
+ * Return <0 for error
+ */
+static int unlock_full_stripe(struct btrfs_fs_info *fs_info, u64 bytenr)
+{
+ struct btrfs_block_group_cache *bg_cache;
+ struct btrfs_full_stripe_locks_tree *locks_root;
+ struct full_stripe_lock *fstripe_lock;
+ u64 fstripe_start;
+ bool freeit = false;
+ int ret = 0;
+
+ bg_cache = btrfs_lookup_block_group(fs_info, bytenr);
+ if (!bg_cache)
+ return -ENOENT;
Ditto.
+ if (!(bg_cache->flags & BTRFS_BLOCK_GROUP_RAID56_MASK))
+ goto out;
+
+ locks_root = &bg_cache->full_stripe_locks_root;
+ ret = get_full_stripe_logical(fs_info, bytenr, &fstripe_start);
+ if (ret < 0)
+ goto out;
+
+ mutex_lock(&locks_root->lock);
+ fstripe_lock = search_full_stripe_lock(locks_root, fstripe_start);
+ /* Unparied unlock_full_stripe() detected */
* unpaired *
+ if (WARN_ON(!fstripe_lock)) {
+ ret = -ENOENT;
+ mutex_unlock(&locks_root->lock);
+ goto out;
+ }
+
+ if (fstripe_lock->refs == 0) {
+ WARN_ON(1);
+ btrfs_warn(fs_info, "full stripe lock at %llu refcount underflow",
+ fstripe_lock->logical);
+ } else
+ fstripe_lock->refs--;
This is error-prone, could you please change it to the following?
} else {
fstripe_lock->refs--;
}
Right, I'll add back the bracket.
Thanks for the review,
Qu
Reviewed-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
Thanks,
-liubo
+ if (fstripe_lock->refs == 0) {
+ rb_erase(&fstripe_lock->node, &locks_root->root);
+ freeit = true;
+ }
+ mutex_unlock(&locks_root->lock);
+
+ mutex_unlock(&fstripe_lock->mutex);
+ if (freeit)
+ kfree(fstripe_lock);
+out:
+ btrfs_put_block_group(bg_cache);
+ return ret;
+}
+
+/*
* used for workers that require transaction commits (i.e., for the
* NOCOW case)
*/
--
2.12.1
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