mirror_zfs/module
Andriy Tkachuk f8457fbdc4
Fix deadlock on dmu_tx_assign() from vdev_rebuild()
vdev_rebuild() is always called with spa_config_lock held in
RW_WRITER mode. However, when it tries to call dmu_tx_assign()
the latter may hang on dmu_tx_wait() waiting for available txg.
But that available txg may not happen because txg_sync takes
spa_config_lock in order to process the current txg. So we have
a deadlock case here:

 - dmu_tx_assign() waits for txg holding spa_config_lock;
 - txg_sync waits for spa_config_lock not progressing with txg.

Here are the stacks:

    __schedule+0x24e/0x590
    schedule+0x69/0x110
    cv_wait_common+0xf8/0x130 [spl]
    __cv_wait+0x15/0x20 [spl]
    dmu_tx_wait+0x8e/0x1e0 [zfs]
    dmu_tx_assign+0x49/0x80 [zfs]
    vdev_rebuild_initiate+0x39/0xc0 [zfs]
    vdev_rebuild+0x84/0x90 [zfs]
    spa_vdev_attach+0x305/0x680 [zfs]
    zfs_ioc_vdev_attach+0xc7/0xe0 [zfs]

    cv_wait_common+0xf8/0x130 [spl]
    __cv_wait+0x15/0x20 [spl]
    spa_config_enter+0xf9/0x120 [zfs]
    spa_sync+0x6d/0x5b0 [zfs]
    txg_sync_thread+0x266/0x2f0 [zfs]

The solution is to pass txg returned by spa_vdev_enter(spa)
at the top of spa_vdev_attach() to vdev_rebuild() and call
dmu_tx_create_assigned(txg) which doesn't wait for txg.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Akash B <akash-b@hpe.com>
Reviewed-by: Alek Pinchuk <apinchuk@axcient.com>
Signed-off-by: Andriy Tkachuk <andriy.tkachuk@seagate.com>
Closes #18210
Closes #18258
2026-02-26 11:18:02 -08:00
..
avl Prefer VERIFY0P(n) over VERIFY(n == NULL) 2025-08-07 11:41:37 -07:00
icp icp: add SHA512 implementation using Intel SHA512 extensions 2026-02-25 12:48:30 -08:00
lua SPDX: license tags: MIT 2025-03-13 17:56:54 -07:00
nvpair nvpair: chase FreeBSD xdrproc_t definition 2026-01-28 21:41:33 -05:00
os zpl_super: prefer "new" mount API when available 2026-02-25 13:17:33 -08:00
zcommon simd: detect and surface support for Intel SHA512 extensions 2026-02-25 12:47:48 -08:00
zfs Fix deadlock on dmu_tx_assign() from vdev_rebuild() 2026-02-26 11:18:02 -08:00
zstd Zstd: Document update policy 2026-01-20 13:41:24 -08:00
.gitignore FreeBSD: Ignore symlink to i386 includes 2022-08-02 16:34:23 -07:00
Kbuild.in Zstd: Integrate v1.5.7 into the ZFS build system 2026-01-20 13:41:06 -08:00
Makefile.bsd Zstd: Integrate v1.5.7 into the ZFS build system 2026-01-20 13:41:06 -08:00
Makefile.in Fix --enable-invariants on FreeBSD 2026-01-14 14:54:12 -08:00