mm/zswap: use workqueue to destroy pool
Add a work_struct to struct zswap_pool, and change __zswap_pool_empty to use the workqueue instead of using call_rcu(). When zswap destroys a pool no longer in use, it uses call_rcu() to perform the destruction/freeing. Since that executes in softirq context, it must not sleep. However, actually destroying the pool involves freeing the per-cpu compressors (which requires locking the cpu_add_remove_lock mutex) and freeing the zpool, for which the implementation may sleep (e.g. zsmalloc calls kmem_cache_destroy, which locks the slab_mutex). So if either mutex is currently taken, or any other part of the compressor or zpool implementation sleeps, it will result in a BUG(). It's not easy to reproduce this when changing zswap's params normally. In testing with a loaded system, this does not fail: $ cd /sys/module/zswap/parameters $ echo lz4 > compressor ; echo zsmalloc > zpool nor does this: $ while true ; do > echo lzo > compressor ; echo zbud > zpool > sleep 1 > echo lz4 > compressor ; echo zsmalloc > zpool > sleep 1 > done although it's still possible either of those might fail, depending on whether anything else besides zswap has locked the mutexes. However, changing a parameter with no delay immediately causes the schedule while atomic BUG: $ while true ; do > echo lzo > compressor ; echo lz4 > compressor > done This is essentially the same as Yu Zhao's proposed patch to zsmalloc, but moved to zswap, to cover compressor and zpool freeing. Fixes: f1c54846 ("zswap: dynamic pool creation") Signed-off-by:Dan Streetman <ddstreet@ieee.org> Reported-by:
Yu Zhao <yuzhao@google.com> Reviewed-by:
Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Dan Streetman <dan.streetman@canonical.com> Signed-off-by:
Andrew Morton <akpm@linux-foundation.org> Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org>
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