Tejun Heo wrote:
Hi, Jeff.
Jeff Garzik wrote:
Tejun Heo wrote:
Both all the list-heads need to be cleared, otherwise there may be
list corruption next time the element is added to the list_head.
scmd->eh_entry is never used as list head. It's always used as list
entry. So, technically, it needs not be cleared, I think. No? The
problem we had was w/ shost->eh_cmd_q not being cleared.
Every node is a list_head. You want all pointers for all nodes
pointing to something useful, even if they are not actively present on
a list, so that they may be easily and corrected added to a list at a
later time. Read list_del_init() for example.
Jeff
Okay... to make things clearer. A struct list_head can have two roles.
list head : other list_head gets added to it
list entry : gets added to other list_head
When a struct list_head acts as list head, it always needs to be in
clean (pointing to valid things) state before being used. When a struct
list_head acts as list entry, its current content doesn't matter.
AFAICS, scmd->eh_entry is currently not used as list head in any place,
neither do we use list_empty() test on it to determine whether or not
it's on a list. The original code does clear scmd->eh_entry all the
time and I am very okay with that. I just wanted to make sure that I
didn't miss something regarding scmd->eh_entry's usage.
If I'm missing such a usage, can you please point out?
I'm mainly talking at a higher level. While it strictly doesn't matter
in this instance, in general its a bad idea to clear a list using a
list = (null)
operation. Its a good way to leak references, leak memory, etc.
In this specific case it seems to be OK.
Jeff
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