Fix txg_quiesce thread deadlock #1428
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A deadlock was accidentally introduced by commit e95853a which can occur when the system is under memory pressure. What happens is that while the txg_quiesce thread is holding the tx->tx_cpu locks it enters memory reclaim. In the context of this memory reclaim it then issues synchronous I/O to a ZVOL swap device. Because the txg_quiesce thread is holding the tx->tx_cpu locks a new txg cannot be opened to handle the I/O. Deadlock. The fix is straight forward. Move the memory allocation outside the critical region where the tx->tx_cpu locks are held. And for good measure change the offending allocation to KM_PUSHPAGE to ensure it never attempts to issue I/O during reclaim. Signed-off-by: Brian Behlendorf <[email protected]> Issue openzfs#1274
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57f5a20 Fix txg_quiesce thread deadlock |
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A deadlock was accidentally introduced by commit e95853a which
can occur when the system is under memory pressure. What happens
is that while the txg_quiesce thread is holding the tx->tx_cpu
locks it enters memory reclaim. In the context of this memory
reclaim it then issues synchronous I/O to a ZVOL swap device.
Because the txg_quiesce thread is holding the tx->tx_cpu locks
a new txg cannot be opened to handle the I/O. Deadlock.
The fix is straight forward. Move the memory allocation outside
the critical region where the tx->tx_cpu locks are held. And for
good measure change the offending allocation to KM_PUSHPAGE to
ensure it never attempts to issue I/O during reclaim.
Signed-off-by: Brian Behlendorf [email protected]
Issue #1274