Hi Andrew, Please see inlined comment below (I found a bug and replied to the original patch with v2 but wasn't quick enough). On Mon, Feb 24, 2025 at 06:26:10PM -0800, Andrew Morton wrote: > > The patch titled > Subject: NFS: fix nfs_release_folio() to not call nfs_wb_folio() from kcompactd > has been added to the -mm mm-hotfixes-unstable branch. Its filename is > nfs-fix-nfs_release_folio-to-not-call-nfs_wb_folio-from-kcompactd.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-call-nfs_wb_folio-from-kcompactd.patch > > This patch will later appear in the mm-hotfixes-unstable branch at > git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm > > Before you just go and hit "reply", please: > a) Consider who else should be cc'ed > b) Prefer to cc a suitable mailing list as well > c) Ideally: find the original patch on the mailing list and do a > reply-to-all to that, adding suitable additional cc's > > *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** > > The -mm tree is included into linux-next via the mm-everything > branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm > and is updated there every 2-3 working days > > ------------------------------------------------------ > From: Mike Snitzer <snitzer@xxxxxxxxxx> > Subject: NFS: fix nfs_release_folio() to not call nfs_wb_folio() from kcompactd > Date: Mon, 24 Feb 2025 19:33:01 -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 induced 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/20250225003301.25693-1-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-call-nfs_wb_folio-from-kcompactd > +++ 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-call-nfs_wb_folio-from-kcompactd > +++ 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-call-nfs_wb_folio-from-kcompactd > +++ 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-call-nfs_wb_folio-from-kcompactd > +++ 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; This should be: tsk->flags |= PF_KCOMPACTD; Sorry for the trouble, v2 is available here: https://lore.kernel.org/linux-nfs/20250225022002.26141-1-snitzer@xxxxxxxxxx/ > 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-call-nfs_wb_folio-from-kcompactd.patch >
