Messages in this thread | | | Date | Thu, 6 Feb 2020 17:38:44 +0100 | From | "Jason A. Donenfeld" <> | Subject | Re: [PATCH v3] skbuff: fix a data race in skb_queue_len() |
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Hi Eric,
On Tue, Feb 04, 2020 at 01:40:29PM -0500, Qian Cai wrote: > - list->qlen--; > + WRITE_ONCE(list->qlen, list->qlen - 1);
Sorry I'm a bit late to the party here, but this immediately jumped out. This generates worse code with a bigger race in some sense:
list->qlen-- is:
0: 83 6f 10 01 subl $0x1,0x10(%rdi)
whereas WRITE_ONCE(list->qlen, list->qlen - 1) is:
0: 8b 47 10 mov 0x10(%rdi),%eax 3: 83 e8 01 sub $0x1,%eax 6: 89 47 10 mov %eax,0x10(%rdi)
Are you sure that's what we want?
Jason
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