Commit cce0be6e authored by Trond Myklebust's avatar Trond Myklebust
Browse files

NFS: Fix a deadlock involving nfs_release_folio() 



Wang Zhaolong reports a deadlock involving NFSv4.1 state recovery
waiting on kthreadd, which is attempting to reclaim memory by calling
nfs_release_folio(). The latter cannot make progress due to state
recovery being needed.

It seems that the only safe thing to do here is to kick off a writeback
of the folio, without waiting for completion, or else kicking off an
asynchronous commit.

Reported-by: default avatarWang Zhaolong <wangzhaolong@huaweicloud.com>
Fixes: 96780ca5 ("NFS: fix up nfs_release_folio() to try to release the page")
Signed-off-by: default avatarTrond Myklebust <trond.myklebust@hammerspace.com>
parent 857bf905

fs/nfs/file.c

+2 −1
Original line number Diff line number Diff line
@@ -511,7 +511,8 @@ static bool nfs_release_folio(struct folio *folio, gfp_t gfp) 
		if ((current_gfp_context(gfp) & GFP_KERNEL) != GFP_KERNEL ||

		    current_is_kswapd() || current_is_kcompactd())

			return false;

		if (nfs_wb_folio(folio->mapping->host, folio) < 0)

		if (nfs_wb_folio_reclaim(folio->mapping->host, folio) < 0 ||

		    folio_test_private(folio))

			return false;

	}

	return nfs_fscache_release_folio(folio, gfp);

fs/nfs/nfstrace.h

+3 −0
Original line number Diff line number Diff line
@@ -1062,6 +1062,9 @@ DECLARE_EVENT_CLASS(nfs_folio_event_done, 
DEFINE_NFS_FOLIO_EVENT(nfs_aop_readpage);

DEFINE_NFS_FOLIO_EVENT_DONE(nfs_aop_readpage_done);



DEFINE_NFS_FOLIO_EVENT(nfs_writeback_folio_reclaim);

DEFINE_NFS_FOLIO_EVENT_DONE(nfs_writeback_folio_reclaim_done);



DEFINE_NFS_FOLIO_EVENT(nfs_writeback_folio);

DEFINE_NFS_FOLIO_EVENT_DONE(nfs_writeback_folio_done);

fs/nfs/write.c

+33 −0
Original line number Diff line number Diff line
@@ -2024,6 +2024,39 @@ int nfs_wb_folio_cancel(struct inode *inode, struct folio *folio) 
	return ret;

}



/**

 * nfs_wb_folio_reclaim - Write back all requests on one page

 * @inode: pointer to page

 * @folio: pointer to folio

 *

 * Assumes that the folio has been locked by the caller

 */

int nfs_wb_folio_reclaim(struct inode *inode, struct folio *folio)

{

	loff_t range_start = folio_pos(folio);

	size_t len = folio_size(folio);

	struct writeback_control wbc = {

		.sync_mode = WB_SYNC_ALL,

		.nr_to_write = 0,

		.range_start = range_start,

		.range_end = range_start + len - 1,

		.for_sync = 1,

	};

	int ret;



	if (folio_test_writeback(folio))

		return -EBUSY;

	if (folio_clear_dirty_for_io(folio)) {

		trace_nfs_writeback_folio_reclaim(inode, range_start, len);

		ret = nfs_writepage_locked(folio, &wbc);

		trace_nfs_writeback_folio_reclaim_done(inode, range_start, len,

						       ret);

		return ret;

	}

	nfs_commit_inode(inode, 0);

	return 0;

}



/**

 * nfs_wb_folio - Write back all requests on one page

 * @inode: pointer to page

include/linux/nfs_fs.h

+1 −0
Original line number Diff line number Diff line
@@ -637,6 +637,7 @@ extern int nfs_update_folio(struct file *file, struct folio *folio, 
extern int nfs_sync_inode(struct inode *inode);

extern int nfs_wb_all(struct inode *inode);

extern int nfs_wb_folio(struct inode *inode, struct folio *folio);

extern int nfs_wb_folio_reclaim(struct inode *inode, struct folio *folio);

int nfs_wb_folio_cancel(struct inode *inode, struct folio *folio);

extern int  nfs_commit_inode(struct inode *, int);

extern struct nfs_commit_data *nfs_commitdata_alloc(void);