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NFS: fix nfs_release_folio() to not deadlock via kcompactd writeback

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commit ce6d9c1c2b upstream.

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
---}

[akpm@linux-foundation.org: fix build]
Link: https://lkml.kernel.org/r/20250225022002.26141-1-snitzer@kernel.org
Fixes: 96780ca55e ("NFS: fix up nfs_release_folio() to try to release the page")
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Cc: Anna Schumaker <anna.schumaker@oracle.com>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Mike Snitzer 2025-02-24 21:20:02 -05:00 committed by Greg Kroah-Hartman
parent 272abd47f7
commit ab0727d6e2
4 changed files with 11 additions and 2 deletions
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3
fs/nfs/file.c
View File

@ -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>
@ -450,7 +451,7 @@ static bool nfs_release_folio(struct folio *folio, gfp_t gfp)
/* 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_file_mapping(folio)->host, folio) < 0)
return false;

5
include/linux/compaction.h
View File

@ -80,6 +80,11 @@ static inline unsigned long compact_gap(unsigned int order)
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);

2
include/linux/sched.h
View File

@ -1746,7 +1746,7 @@ 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 allocation requests will inherit GFP_NOFS */
#define PF_MEMALLOC_NOIO 0x00080000 /* All allocation requests will inherit GFP_NOIO */

3
mm/compaction.c
View File

@ -3050,6 +3050,7 @@ static int kcompactd(void *p)
if (!cpumask_empty(cpumask))
set_cpus_allowed_ptr(tsk, cpumask);
current->flags |= PF_KCOMPACTD;
set_freezable();
pgdat->kcompactd_max_order = 0;
@ -3106,6 +3107,8 @@ static int kcompactd(void *p)
pgdat->proactive_compact_trigger = false;
}
current->flags &= ~PF_KCOMPACTD;
return 0;
}