For efficiency reasons, zsmalloc is using a slim `handle'. The value is the address of a memory allocation of 4 or 8 bytes depending on the size of the long data type. The lowest bit in that allocated memory is used as a bit spin lock. The usage of the bit spin lock is problematic because with the bit spin lock held zsmalloc acquires a rwlock_t and spinlock_t which are both sleeping locks on PREEMPT_RT and therefore must not be acquired with disabled preemption. There is a patch which extends the handle on PREEMPT_RT so that a full spinlock_t fits (even with lockdep enabled) and then eliminates the bit spin lock. I'm not sure how sensible zsmalloc on PREEMPT_RT is given that it is used to store compressed user memory. Disable ZSMALLOC on PREEMPT_RT. If there is need for it, we can try to get it to work. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> --- mm/Kconfig | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/Kconfig b/mm/Kconfig index 9f1e0098522c2..541371e64c477 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -640,6 +640,7 @@ config ZSWAP_ZPOOL_DEFAULT_Z3FOLD config ZSWAP_ZPOOL_DEFAULT_ZSMALLOC bool "zsmalloc" + depends on !PREEMPT_RT select ZSMALLOC help Use the zsmalloc allocator as the default allocator. @@ -690,7 +691,7 @@ config Z3FOLD config ZSMALLOC tristate "Memory allocator for compressed pages" - depends on MMU + depends on MMU && !PREEMPT_RT help zsmalloc is a slab-based memory allocator designed to store compressed RAM pages. zsmalloc uses virtual memory mapping -- 2.33.0
