The patch titled
Subject: NFS: fix nfs_release_folio() to not deadlock via kcompactd writeback
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
nfs-fix-nfs_release_folio-to-not-deadlock-via-kcompactd-writeback.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/nfs-fix-nfs_release_folio-to-not-deadlock-via-kcompactd-writeback.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Mike Snitzer <snitzer@xxxxxxxxxx>
Subject: NFS: fix nfs_release_folio() to not deadlock via kcompactd writeback
Date: Mon, 24 Feb 2025 21:20:02 -0500
Add PF_KCOMPACTD flag and current_is_kcompactd() helper to check for it so
nfs_release_folio() can skip calling nfs_wb_folio() from kcompactd.
Otherwise NFS can deadlock waiting for kcompactd enduced writeback which
recurses back to NFS (which triggers writeback to NFSD via NFS loopback
mount on the same host, NFSD blocks waiting for XFS's call to
__filemap_get_folio):
6070.550357] INFO: task kcompactd0:58 blocked for more than 4435 seconds.
{---
[58] "kcompactd0"
[<0>] folio_wait_bit+0xe8/0x200
[<0>] folio_wait_writeback+0x2b/0x80
[<0>] nfs_wb_folio+0x80/0x1b0 [nfs]
[<0>] nfs_release_folio+0x68/0x130 [nfs]
[<0>] split_huge_page_to_list_to_order+0x362/0x840
[<0>] migrate_pages_batch+0x43d/0xb90
[<0>] migrate_pages_sync+0x9a/0x240
[<0>] migrate_pages+0x93c/0x9f0
[<0>] compact_zone+0x8e2/0x1030
[<0>] compact_node+0xdb/0x120
[<0>] kcompactd+0x121/0x2e0
[<0>] kthread+0xcf/0x100
[<0>] ret_from_fork+0x31/0x40
[<0>] ret_from_fork_asm+0x1a/0x30
---}
Link: https://lkml.kernel.org/r/20250225022002.26141-1-snitzer@xxxxxxxxxx
Fixes: 96780ca55e3cb ("NFS: fix up nfs_release_folio() to try to release the page")
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Cc: Anna Schumaker <anna.schumaker@xxxxxxxxxx>
Cc: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/nfs/file.c | 3 ++-
include/linux/compaction.h | 5 +++++
include/linux/sched.h | 2 +-
mm/compaction.c | 3 +++
4 files changed, 11 insertions(+), 2 deletions(-)
--- a/fs/nfs/file.c~nfs-fix-nfs_release_folio-to-not-deadlock-via-kcompactd-writeback
+++ a/fs/nfs/file.c
@@ -29,6 +29,7 @@
#include <linux/pagemap.h>
#include <linux/gfp.h>
#include <linux/swap.h>
+#include <linux/compaction.h>
#include <linux/uaccess.h>
#include <linux/filelock.h>
@@ -457,7 +458,7 @@ static bool nfs_release_folio(struct fol
/* If the private flag is set, then the folio is not freeable */
if (folio_test_private(folio)) {
if ((current_gfp_context(gfp) & GFP_KERNEL) != GFP_KERNEL ||
- current_is_kswapd())
+ current_is_kswapd() || current_is_kcompactd())
return false;
if (nfs_wb_folio(folio->mapping->host, folio) < 0)
return false;
--- a/include/linux/compaction.h~nfs-fix-nfs_release_folio-to-not-deadlock-via-kcompactd-writeback
+++ a/include/linux/compaction.h
@@ -80,6 +80,11 @@ static inline unsigned long compact_gap(
return 2UL << order;
}
+static inline int current_is_kcompactd(void)
+{
+ return current->flags & PF_KCOMPACTD;
+}
+
#ifdef CONFIG_COMPACTION
extern unsigned int extfrag_for_order(struct zone *zone, unsigned int order);
--- a/include/linux/sched.h~nfs-fix-nfs_release_folio-to-not-deadlock-via-kcompactd-writeback
+++ a/include/linux/sched.h
@@ -1701,7 +1701,7 @@ extern struct pid *cad_pid;
#define PF_USED_MATH 0x00002000 /* If unset the fpu must be initialized before use */
#define PF_USER_WORKER 0x00004000 /* Kernel thread cloned from userspace thread */
#define PF_NOFREEZE 0x00008000 /* This thread should not be frozen */
-#define PF__HOLE__00010000 0x00010000
+#define PF_KCOMPACTD 0x00010000 /* I am kcompactd */
#define PF_KSWAPD 0x00020000 /* I am kswapd */
#define PF_MEMALLOC_NOFS 0x00040000 /* All allocations inherit GFP_NOFS. See memalloc_nfs_save() */
#define PF_MEMALLOC_NOIO 0x00080000 /* All allocations inherit GFP_NOIO. See memalloc_noio_save() */
--- a/mm/compaction.c~nfs-fix-nfs_release_folio-to-not-deadlock-via-kcompactd-writeback
+++ a/mm/compaction.c
@@ -3181,6 +3181,7 @@ static int kcompactd(void *p)
long default_timeout = msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC);
long timeout = default_timeout;
+ tsk->flags |= PF_KCOMPACTD;
set_freezable();
pgdat->kcompactd_max_order = 0;
@@ -3237,6 +3238,8 @@ static int kcompactd(void *p)
pgdat->proactive_compact_trigger = false;
}
+ tsk->flags &= ~PF_KCOMPACTD;
+
return 0;
}
_
Patches currently in -mm which might be from snitzer@xxxxxxxxxx are
nfs-fix-nfs_release_folio-to-not-deadlock-via-kcompactd-writeback.patch
