CVE-2025-21908 Information

Description

In the Linux kernel the following vulnerability has been resolved:

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

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\n[<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]

Reference

https://git.kernel.org/stable/c/5ae31c54cff745832b9bd5b32e71f3d1b607cd1e https://git.kernel.org/stable/c/8253ff29edcb429a9a6c75710941c6a16a9a34b1 https://git.kernel.org/stable/c/ab0727d6e2196682351c25c1dd112136f6991f11 https://git.kernel.org/stable/c/ce6d9c1c2b5cc785016faa11b48b6cd317eb367e