Messages in this thread | | | Date | Tue, 12 Dec 2017 14:45:07 +0000 | From | Mark Rutland <> | Subject | Re: [PATCHv2] virtio_mmio: fix devm cleanup |
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On Tue, Dec 12, 2017 at 10:26:24PM +0800, weiping zhang wrote: > 2017-12-12 21:45 GMT+08:00 Mark Rutland <mark.rutland@arm.com>: > Hi Mark,
Hi,
> thanks your patch, I dig into these three devm_xxx funciton, > all of them represented by a struct devres as following, > > struct devres_node { > struct list_head entry; > dr_release_t release; > #ifdef CONFIG_DEBUG_DEVRES > const char *name; > size_t size; > #endif > > }; > > struct devres { > struct devres_node node; > /* -- 3 pointers */ > unsigned long long data[]; /* guarantee ull alignment */ > };
> 2) devm_kzalloc -> devm_kmalloc > > dr = alloc_dr(devm_kmalloc_release, size, gfp, dev_to_node(dev)); > "devm_kmalloc_release" is noop, do nothing.
Please note that the release function is there to perform cleanup prior to the devm infrastructure releasing the memory.
The devm_kmalloc_release function is a no-op since nothing has to be done prior to memory being freed, but the memory itself is still freed.
In alloc_dr(), the struct devres is allocated together with the memory, since alloc_dr() does:
size_t tot_size = sizeof(struct devres) + size; struct devres *dr;
dr = kmalloc_node_track_caller(tot_size, gfp, nid);
return dr->data;
... where dr->data points at the memory after the struct devres.
Later, in release_nodes() we do:
list_for_each_entry_safe_reverse(dr, tmp, &todo, node.entry) { devres_log(dev, &dr->node, "REL"); dr->node.release(dev, dr->data); kfree(dr); }
... which will invoke the no-op devm_kmalloc_release, then free the devres allocation, including the dr->data memory the user requested.
> so for case 2) above, we need a devm_kfree() before call > register_virtio_device
As above, I do not believe that is the case.
Thanks, Mark.
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