pNFS: Fix a deadlock when returning a delegation during open()

Overview

In the Linux kernel, the following vulnerability has been resolved:

pNFS: Fix a deadlock when returning a delegation during open()

Ben Coddington reports seeing a hang in the following stack trace: 0 [ffffd0b50e1774e0] __schedule at ffffffff9ca05415 1 [ffffd0b50e177548] schedule at ffffffff9ca05717 2 [ffffd0b50e177558] bit_wait at ffffffff9ca061e1 3 [ffffd0b50e177568] __wait_on_bit at ffffffff9ca05cfb 4 [ffffd0b50e1775c8] out_of_line_wait_on_bit at ffffffff9ca05ea5 5 [ffffd0b50e177618] pnfs_roc at ffffffffc154207b [nfsv4] 6 [ffffd0b50e1776b8] _nfs4_proc_delegreturn at ffffffffc1506586 [nfsv4] 7 [ffffd0b50e177788] nfs4_proc_delegreturn at ffffffffc1507480 [nfsv4] 8 [ffffd0b50e1777f8] nfs_do_return_delegation at ffffffffc1523e41 [nfsv4] 9 [ffffd0b50e177838] nfs_inode_set_delegation at ffffffffc1524a75 [nfsv4] 10 [ffffd0b50e177888] nfs4_process_delegation at ffffffffc14f41dd [nfsv4] 11 [ffffd0b50e1778a0] _nfs4_opendata_to_nfs4_state at ffffffffc1503edf [nfsv4] 12 [ffffd0b50e1778c0] _nfs4_open_and_get_state at ffffffffc1504e56 [nfsv4] 13 [ffffd0b50e177978] _nfs4_do_open at ffffffffc15051b8 [nfsv4] 14 [ffffd0b50e1779f8] nfs4_do_open at ffffffffc150559c [nfsv4] 15 [ffffd0b50e177a80] nfs4_atomic_open at ffffffffc15057fb [nfsv4] 16 [ffffd0b50e177ad0] nfs4_file_open at ffffffffc15219be [nfsv4] 17 [ffffd0b50e177b78] do_dentry_open at ffffffff9c09e6ea 18 [ffffd0b50e177ba8] vfs_open at ffffffff9c0a082e 19 [ffffd0b50e177bd0] dentry_open at ffffffff9c0a0935

The issue is that the delegreturn is being asked to wait for a layout return that cannot complete because a state recovery was initiated. The state recovery cannot complete until the open() finishes processing the delegations it was given.

The solution is to propagate the existing flags that indicate a non-blocking call to the function pnfs_roc(), so that it knows not to wait in this situation.

Affected

• Linux >= 29ade5db12930ec60133f6a02791f4b1a4af2943 < 05a685b38dbca489d5f21eac9e7f20959344076a
• Linux >= 29ade5db12930ec60133f6a02791f4b1a4af2943 < c57387d447a2bcbaea009ba5f9497adf3de5edeb
• Linux >= 29ade5db12930ec60133f6a02791f4b1a4af2943 < a316fd9d3065b753b03d802530004aea481512cc
• Linux >= 29ade5db12930ec60133f6a02791f4b1a4af2943 < d6c75aa9d607044d1e5c8498eff0259eed356c32
• Linux >= 29ade5db12930ec60133f6a02791f4b1a4af2943 < 857bf9056291a16785ae3be1d291026b2437fc48
• Linux 4.10

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.