Alison Schofield 8d4b989d9c nvdimm/btt: Handle preemption in BTT lane acquisition ...

BTT lanes serialize access to per-lane metadata and workspace state
during BTT I/O. The btt-check unit test reports data mismatches during
BTT writes due to a race in lane acquisition that can lead to silent
data corruption.

The existing lane model uses a spinlock together with a per-CPU
recursion count. That recursion model stopped being valid after BTT
lanes became preemptible: another task can run on the same CPU,
observe a non-zero recursion count, bypass locking, and use the same
lane concurrently.

BTT lanes are also held across arena_write_bytes() calls. That path
reaches nsio_rw_bytes(), which flushes writes with nvdimm_flush().
Some provider flush callbacks can sleep, making a spinlock the wrong
primitive for the lane lifetime.

Replace the spinlock-based recursion model with a dynamically
allocated per-lane mutex array and take the lane lock
unconditionally.

Add might_sleep() to catch any future atomic-context caller.

Found with the ndctl unit test btt-check.sh.

Fixes: 36c75ce3bd ("nd_btt: Make BTT lanes preemptible")
Assisted-by: Claude-Sonnet:4.5
Tested-by: Aboorva Devarajan <[email protected]>
Reviewed-by: Aboorva Devarajan <[email protected]>
Reviewed-by: Vishal Verma <[email protected]>
Reviewed-by: Dave Jiang <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Alison Schofield <[email protected]>

2026-06-01 13:53:24 -07:00

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btt.rst

nvdimm/btt: Handle preemption in BTT lane acquisition

2026-06-01 13:53:24 -07:00

firmware-activate.rst

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index.rst

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nvdimm.rst

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security.rst

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