Merge pull request #2402 from flatcar/dongsu/ext4-deadlock-fix-3374

sys-kernel/coreos-sources: Add backport of bugfix for #847 for flatcar-3374

changelog/bugfixes/2023-01-19-kernel-bug-847.md

@@ -0,0 +1 @@
+- Fix "ext4 deadlock under heavy I/O load" kernel issue. The patch for this is included provisionally while we stay with Kernel 5.15.86. ([Flatcar#847](https://github.com/flatcar/Flatcar/issues/847), [coreos-overlay#2402](https://github.com/flatcar/coreos-overlay/pull/2402))

sys-kernel/coreos-sources/coreos-sources-5.15.86.ebuild

@@ -42,4 +42,5 @@ UNIPATCH_LIST="
 	${PATCH_DIR}/z0005-Drivers-hv-vmbus-Propagate-VMbus-coherence-to-each-V.patch \
 	${PATCH_DIR}/z0006-PCI-hv-Avoid-the-retarget-interrupt-hypercall-in-irq.patch \
 	${PATCH_DIR}/z0007-PCI-hv-Remove-unused-hv_set_msi_entry_from_desc.patch \
+	${PATCH_DIR}/z0008-ext4-Fix-deadlock-due-to-mbcache-en.patch \
 "

sys-kernel/coreos-sources/files/5.15/z0008-ext4-Fix-deadlock-due-to-mbcache-en.patch

@@ -0,0 +1,129 @@
+From e7ec42e181c6213d1fd71b946196f05af601ba5c Mon Sep 17 00:00:00 2001
+From: Jan Kara <[email protected]>
+Date: Mon, 21 Nov 2022 15:44:10 +0100
+Subject: [PATCH] ext4: Fix deadlock due to mbcache entry corruption
+
+When manipulating xattr blocks, we can deadlock infinitely looping
+inside ext4_xattr_block_set() where we constantly keep finding xattr
+block for reuse in mbcache but we are unable to reuse it because its
+reference count is too big. This happens because cache entry for the
+xattr block is marked as reusable (e_reusable set) although its
+reference count is too big. When this inconsistency happens, this
+inconsistent state is kept indefinitely and so ext4_xattr_block_set()
+keeps retrying indefinitely.
+
+The inconsistent state is caused by non-atomic update of e_reusable bit.
+e_reusable is part of a bitfield and e_reusable update can race with
+update of e_referenced bit in the same bitfield resulting in loss of one
+of the updates. Fix the problem by using atomic bitops instead.
+
+[jeremi: backport from here https://lore.kernel.org/linux-ext4/20221122174807.GA9658@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net/]
+CC: [email protected]
+Fixes: 6048c64b2609 ("mbcache: add reusable flag to cache entries")
+Reported-by: Jeremi Piotrowski <[email protected]>
+Reported-by: Thilo Fromm <[email protected]>
+Signed-off-by: Jan Kara <[email protected]>
+---
+ fs/ext4/xattr.c         |  4 ++--
+ fs/mbcache.c            | 14 ++++++++------
+ include/linux/mbcache.h |  9 +++++++--
+ 3 files changed, 17 insertions(+), 10 deletions(-)
+
+diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
+index 533216e80fa2..22700812a4d3 100644
+--- a/fs/ext4/xattr.c
++++ b/fs/ext4/xattr.c
+@@ -1281,7 +1281,7 @@ ext4_xattr_release_block(handle_t *handle, struct inode *inode,
+ 				ce = mb_cache_entry_get(ea_block_cache, hash,
+ 							bh->b_blocknr);
+ 				if (ce) {
+-					ce->e_reusable = 1;
++					set_bit(MBE_REUSABLE_B, &ce->e_flags);
+ 					mb_cache_entry_put(ea_block_cache, ce);
+ 				}
+ 			}
+@@ -2042,7 +2042,7 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode,
+ 				}
+ 				BHDR(new_bh)->h_refcount = cpu_to_le32(ref);
+ 				if (ref == EXT4_XATTR_REFCOUNT_MAX)
+-					ce->e_reusable = 0;
++					clear_bit(MBE_REUSABLE_B, &ce->e_flags);
+ 				ea_bdebug(new_bh, "reusing; refcount now=%d",
+ 					  ref);
+ 				ext4_xattr_block_csum_set(inode, new_bh);
+diff --git a/fs/mbcache.c b/fs/mbcache.c
+index 2010bc80a3f2..ac07b50ea3df 100644
+--- a/fs/mbcache.c
++++ b/fs/mbcache.c
+@@ -94,8 +94,9 @@ int mb_cache_entry_create(struct mb_cache *cache, gfp_t mask, u32 key,
+ 	atomic_set(&entry->e_refcnt, 1);
+ 	entry->e_key = key;
+ 	entry->e_value = value;
+-	entry->e_reusable = reusable;
+-	entry->e_referenced = 0;
++	entry->e_flags = 0;
++	if (reusable)
++		set_bit(MBE_REUSABLE_B, &entry->e_flags);
+ 	head = mb_cache_entry_head(cache, key);
+ 	hlist_bl_lock(head);
+ 	hlist_bl_for_each_entry(dup, dup_node, head, e_hash_list) {
+@@ -155,7 +156,8 @@ static struct mb_cache_entry *__entry_find(struct mb_cache *cache,
+ 	while (node) {
+ 		entry = hlist_bl_entry(node, struct mb_cache_entry,
+ 				       e_hash_list);
+-		if (entry->e_key == key && entry->e_reusable) {
++		if (entry->e_key == key &&
++		    test_bit(MBE_REUSABLE_B, &entry->e_flags)) {
+ 			atomic_inc(&entry->e_refcnt);
+ 			goto out;
+ 		}
+@@ -325,7 +327,7 @@ EXPORT_SYMBOL(mb_cache_entry_delete_or_get);
+ void mb_cache_entry_touch(struct mb_cache *cache,
+ 			  struct mb_cache_entry *entry)
+ {
+-	entry->e_referenced = 1;
++	set_bit(MBE_REFERENCED_B, &entry->e_flags);
+ }
+ EXPORT_SYMBOL(mb_cache_entry_touch);
+
+@@ -350,8 +352,8 @@ static unsigned long mb_cache_shrink(struct mb_cache *cache,
+ 	while (nr_to_scan-- && !list_empty(&cache->c_list)) {
+ 		entry = list_first_entry(&cache->c_list,
+ 					 struct mb_cache_entry, e_list);
+-		if (entry->e_referenced || atomic_read(&entry->e_refcnt) > 2) {
+-			entry->e_referenced = 0;
++		if (test_bit(MBE_REFERENCED_B, &entry->e_flags) || atomic_read(&entry->e_refcnt) > 2) {
++			clear_bit(MBE_REFERENCED_B, &entry->e_flags);
+ 			list_move_tail(&entry->e_list, &cache->c_list);
+ 			continue;
+ 		}
+diff --git a/include/linux/mbcache.h b/include/linux/mbcache.h
+index 8eca7f25c432..62927f7e2588 100644
+--- a/include/linux/mbcache.h
++++ b/include/linux/mbcache.h
+@@ -10,6 +10,12 @@
+
+ struct mb_cache;
+
++/* Cache entry flags */
++enum {
++	MBE_REFERENCED_B = 0,
++	MBE_REUSABLE_B
++};
++
+ struct mb_cache_entry {
+ 	/* List of entries in cache - protected by cache->c_list_lock */
+ 	struct list_head	e_list;
+@@ -18,8 +24,7 @@ struct mb_cache_entry {
+ 	atomic_t		e_refcnt;
+ 	/* Key in hash - stable during lifetime of the entry */
+ 	u32			e_key;
+-	u32			e_referenced:1;
+-	u32			e_reusable:1;
++	unsigned long		e_flags;
+ 	/* User provided value - stable during lifetime of the entry */
+ 	u64			e_value;
+ };
+-- 
+2.25.1
+