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Konrad Rzeszutek Wilk authored
Commit 10a7a077 ("xen: tmem: enable Xen tmem shim to be built/loaded as a module") allows the tmem module to be loaded any time. For this work the frontswap API had to be able to asynchronously to call tmem_frontswap_init before or after the swap image had been set. That was added in git commit 905cd0e1 ("mm: frontswap: lazy initialization to allow tmem backends to build/run as modules"). Which means we could do this (The common case): modprobe tmem [so calls frontswap_register_ops, no ->init] modifies tmem_frontswap_poolid = -1 swapon /dev/xvda1 [__frontswap_init, calls -> init, tmem_frontswap_poolid is < 0 so tmem hypercall done] Or the failing one: swapon /dev/xvda1 [calls __frontswap_init, sets the need_init bitmap] modprobe tmem [calls frontswap_register_ops, -->init calls, finds out tmem_frontswap_poolid is 0, does not make a hypercall. Later in the module_init, sets tmem_frontswap_poolid=-1] Which meant that in the failing case we would not call the hypercall to initialize the pool and never be able to make any frontswap backend calls. Moving the frontswap_register_ops after setting the tmem_frontswap_poolid fixes it. Signed-off-by:
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Reviewed-by:
Bob Liu <bob.liu@oracle.com>
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