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Merge pull request #2315 from flatcar/bug-847-kernel-fix-backport
sys-kernel/coreos-sources: Add backport of bugfix for #847
This commit is contained in:
Jeremi Piotrowski
GitHub
commit
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1
sdk_container/src/third_party/coreos-overlay/changelog/bugfixes/2022-12-06-kernel-bug-847.md
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sdk_container/src/third_party/coreos-overlay/changelog/bugfixes/2022-12-06-kernel-bug-847.md
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- Fix "ext4 deadlock under heavy I/O load" kernel issue. The patch for this is included provisionally while we wait for it to be merged upstream ([Flatcar#847](https://github.com/flatcar/Flatcar/issues/847), [coreos-overlay#2315](https://github.com/flatcar/coreos-overlay/pull/2315))
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@ -42,4 +42,5 @@ UNIPATCH_LIST="
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${PATCH_DIR}/z0005-Drivers-hv-vmbus-Propagate-VMbus-coherence-to-each-V.patch \
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${PATCH_DIR}/z0006-PCI-hv-Avoid-the-retarget-interrupt-hypercall-in-irq.patch \
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${PATCH_DIR}/z0007-PCI-hv-Remove-unused-hv_set_msi_entry_from_desc.patch \
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${PATCH_DIR}/z0008-ext4-Fix-deadlock-due-to-mbcache-en.patch \
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"
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@ -0,0 +1,129 @@
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From e7ec42e181c6213d1fd71b946196f05af601ba5c Mon Sep 17 00:00:00 2001
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From: Jan Kara <jack@suse.cz>
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Date: Mon, 21 Nov 2022 15:44:10 +0100
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Subject: [PATCH] ext4: Fix deadlock due to mbcache entry corruption
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When manipulating xattr blocks, we can deadlock infinitely looping
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inside ext4_xattr_block_set() where we constantly keep finding xattr
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block for reuse in mbcache but we are unable to reuse it because its
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reference count is too big. This happens because cache entry for the
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xattr block is marked as reusable (e_reusable set) although its
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reference count is too big. When this inconsistency happens, this
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inconsistent state is kept indefinitely and so ext4_xattr_block_set()
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keeps retrying indefinitely.
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The inconsistent state is caused by non-atomic update of e_reusable bit.
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e_reusable is part of a bitfield and e_reusable update can race with
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update of e_referenced bit in the same bitfield resulting in loss of one
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of the updates. Fix the problem by using atomic bitops instead.
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[jeremi: backport from here https://lore.kernel.org/linux-ext4/20221122174807.GA9658@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net/]
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CC: stable@vger.kernel.org
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Fixes: 6048c64b2609 ("mbcache: add reusable flag to cache entries")
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Reported-by: Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>
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Reported-by: Thilo Fromm <t-lo@linux.microsoft.com>
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Signed-off-by: Jan Kara <jack@suse.cz>
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---
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fs/ext4/xattr.c | 4 ++--
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fs/mbcache.c | 14 ++++++++------
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include/linux/mbcache.h | 9 +++++++--
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3 files changed, 17 insertions(+), 10 deletions(-)
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diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
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index 533216e80fa2..22700812a4d3 100644
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--- a/fs/ext4/xattr.c
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+++ b/fs/ext4/xattr.c
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@@ -1281,7 +1281,7 @@ ext4_xattr_release_block(handle_t *handle, struct inode *inode,
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ce = mb_cache_entry_get(ea_block_cache, hash,
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bh->b_blocknr);
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if (ce) {
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- ce->e_reusable = 1;
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+ set_bit(MBE_REUSABLE_B, &ce->e_flags);
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mb_cache_entry_put(ea_block_cache, ce);
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}
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}
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@@ -2042,7 +2042,7 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode,
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}
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BHDR(new_bh)->h_refcount = cpu_to_le32(ref);
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if (ref == EXT4_XATTR_REFCOUNT_MAX)
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- ce->e_reusable = 0;
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+ clear_bit(MBE_REUSABLE_B, &ce->e_flags);
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ea_bdebug(new_bh, "reusing; refcount now=%d",
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ref);
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ext4_xattr_block_csum_set(inode, new_bh);
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diff --git a/fs/mbcache.c b/fs/mbcache.c
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index 2010bc80a3f2..ac07b50ea3df 100644
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--- a/fs/mbcache.c
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+++ b/fs/mbcache.c
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@@ -94,8 +94,9 @@ int mb_cache_entry_create(struct mb_cache *cache, gfp_t mask, u32 key,
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atomic_set(&entry->e_refcnt, 1);
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entry->e_key = key;
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entry->e_value = value;
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- entry->e_reusable = reusable;
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- entry->e_referenced = 0;
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+ entry->e_flags = 0;
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+ if (reusable)
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+ set_bit(MBE_REUSABLE_B, &entry->e_flags);
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head = mb_cache_entry_head(cache, key);
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hlist_bl_lock(head);
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hlist_bl_for_each_entry(dup, dup_node, head, e_hash_list) {
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@@ -155,7 +156,8 @@ static struct mb_cache_entry *__entry_find(struct mb_cache *cache,
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while (node) {
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entry = hlist_bl_entry(node, struct mb_cache_entry,
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e_hash_list);
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- if (entry->e_key == key && entry->e_reusable) {
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+ if (entry->e_key == key &&
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+ test_bit(MBE_REUSABLE_B, &entry->e_flags)) {
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atomic_inc(&entry->e_refcnt);
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goto out;
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}
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@@ -325,7 +327,7 @@ EXPORT_SYMBOL(mb_cache_entry_delete_or_get);
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void mb_cache_entry_touch(struct mb_cache *cache,
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struct mb_cache_entry *entry)
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{
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- entry->e_referenced = 1;
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+ set_bit(MBE_REFERENCED_B, &entry->e_flags);
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}
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EXPORT_SYMBOL(mb_cache_entry_touch);
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@@ -350,8 +352,8 @@ static unsigned long mb_cache_shrink(struct mb_cache *cache,
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while (nr_to_scan-- && !list_empty(&cache->c_list)) {
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entry = list_first_entry(&cache->c_list,
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struct mb_cache_entry, e_list);
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- if (entry->e_referenced || atomic_read(&entry->e_refcnt) > 2) {
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- entry->e_referenced = 0;
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+ if (test_bit(MBE_REFERENCED_B, &entry->e_flags) || atomic_read(&entry->e_refcnt) > 2) {
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+ clear_bit(MBE_REFERENCED_B, &entry->e_flags);
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list_move_tail(&entry->e_list, &cache->c_list);
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continue;
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}
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diff --git a/include/linux/mbcache.h b/include/linux/mbcache.h
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index 8eca7f25c432..62927f7e2588 100644
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--- a/include/linux/mbcache.h
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+++ b/include/linux/mbcache.h
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@@ -10,6 +10,12 @@
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struct mb_cache;
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+/* Cache entry flags */
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+enum {
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+ MBE_REFERENCED_B = 0,
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+ MBE_REUSABLE_B
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+};
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+
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struct mb_cache_entry {
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/* List of entries in cache - protected by cache->c_list_lock */
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struct list_head e_list;
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@@ -18,8 +24,7 @@ struct mb_cache_entry {
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atomic_t e_refcnt;
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/* Key in hash - stable during lifetime of the entry */
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u32 e_key;
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- u32 e_referenced:1;
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- u32 e_reusable:1;
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+ unsigned long e_flags;
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/* User provided value - stable during lifetime of the entry */
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u64 e_value;
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};
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--
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2.25.1
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