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net: fixing a memory leak in if_deregister_com_alloc()

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Drain the callbacks upon if_deregister_com_alloc() such that the
if_com_free[type] won't be nullified before if_destroy().

Taking fwip(4) as an example, before this fix, kldunload if_fwip will
go through the following:

  1. fwip_detach()
  2. if_free() -> schedule if_destroy() through NET_EPOCH_CALL
  3. fwip_detach() returns
  4. firewire_modevent(MOD_UNLOAD) -> if_deregister_com_alloc()
  5. kernel complains about:
	Warning: memory type fw_com leaked memory on destroy (1 allocations, 64 bytes leaked).
  6. EPOCH runs if_destroy() -> if_free_internal()i

By this time, if_com_free[if_alloctype] is NULL since it's already
nullified by if_deregister_com_alloc(); hence, firewire_free() won't
have a chance to release the allocated fw_com.

Reviewed by:	hselasky, glebius
MFC after:	2 weeks
This commit is contained in:
Tai-hwa Liang 2021-03-06 14:36:35 +00:00
parent e797dc58bd
commit 092f3f0812
1 changed files with 8 additions and 0 deletions
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8
sys/net/if.c
View file

@ -4055,6 +4055,14 @@ if_deregister_com_alloc(u_char type)
("if_deregister_com_alloc: %d not registered", type));
KASSERT(if_com_free[type] != NULL,
("if_deregister_com_alloc: %d free not registered", type));
/*
* Ensure all pending EPOCH(9) callbacks have been executed. This
* fixes issues about late invocation of if_destroy(), which leads
* to memory leak from if_com_alloc[type] allocated if_l2com.
*/
epoch_drain_callbacks(net_epoch_preempt);
if_com_alloc[type] = NULL;
if_com_free[type] = NULL;
}