| Message ID | 20250225022002.26141-1-snitzer@kernel.org (mailing list archive) |
|---|---|
| State | Handled Elsewhere |
| Headers | show |
| Series | [v2,for-akpm,for-6.14-rcX] NFS: fix nfs_release_folio() to not deadlock via kcompactd writeback | expand |
On Mon, 24 Feb 2025 21:20:02 -0500 Mike Snitzer <snitzer@kernel.org> wrote: > 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. > --- a/mm/compaction.c~a +++ a/mm/compaction.c @@ -3182,7 +3182,7 @@ static int kcompactd(void *p) long default_timeout = msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC); long timeout = default_timeout; - tsk->flags |= PF_KCOMPACTD; + current->flags |= PF_KCOMPACTD; set_freezable(); pgdat->kcompactd_max_order = 0; @@ -3239,7 +3239,7 @@ static int kcompactd(void *p) pgdat->proactive_compact_trigger = false; } - tsk->flags &= ~PF_KCOMPACTD; + current->flags &= ~PF_KCOMPACTD; return 0; } I am of course concerned about how well tested this was!
On Mon, Feb 24, 2025 at 10:53:06PM -0800, Andrew Morton wrote: > On Mon, 24 Feb 2025 21:20:02 -0500 Mike Snitzer <snitzer@kernel.org> wrote: > > > 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. > > > > --- a/mm/compaction.c~a > +++ a/mm/compaction.c > @@ -3182,7 +3182,7 @@ static int kcompactd(void *p) > long default_timeout = msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC); > long timeout = default_timeout; > > - tsk->flags |= PF_KCOMPACTD; > + current->flags |= PF_KCOMPACTD; > set_freezable(); > > pgdat->kcompactd_max_order = 0; > @@ -3239,7 +3239,7 @@ static int kcompactd(void *p) > pgdat->proactive_compact_trigger = false; > } > > - tsk->flags &= ~PF_KCOMPACTD; > + current->flags &= ~PF_KCOMPACTD; > > return 0; > } > > I am of course concerned about how well tested this was! Understandable, the patch was created and tested against v6.12.16. Sincere apologies, I didn't rebase before submitting. I'll rebase, retest and then send v3 today. Thanks, Mike
diff --git a/fs/nfs/file.c b/fs/nfs/file.c index 1bb646752e466..033feeab8c346 100644 --- a/fs/nfs/file.c +++ b/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 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->mapping->host, folio) < 0) return false; diff --git a/include/linux/compaction.h b/include/linux/compaction.h index e947764960496..7bf0c521db634 100644 --- a/include/linux/compaction.h +++ b/include/linux/compaction.h @@ -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); diff --git a/include/linux/sched.h b/include/linux/sched.h index 8982820dae213..0d1d70aded38f 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1682,7 +1682,7 @@ 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() */ diff --git a/mm/compaction.c b/mm/compaction.c index 384e4672998e5..836c36f9b2f00 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -3164,6 +3164,7 @@ static int kcompactd(void *p) if (!cpumask_empty(cpumask)) set_cpus_allowed_ptr(tsk, cpumask); + tsk->flags |= PF_KCOMPACTD; set_freezable(); pgdat->kcompactd_max_order = 0; @@ -3220,6 +3221,8 @@ static int kcompactd(void *p) pgdat->proactive_compact_trigger = false; } + tsk->flags &= ~PF_KCOMPACTD; + return 0; }
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 ---} Fixes: 96780ca55e3cb ("NFS: fix up nfs_release_folio() to try to release the page") Signed-off-by: Mike Snitzer <snitzer@kernel.org> --- 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(-) v2: use |= to properly set PF_KCOMPACTD in kcompactd(). Also adjust subject to reflect this patch fixes a deadlock.