Messages in this thread | | | Date | Thu, 30 May 2013 09:51:13 +0300 | From | Eliezer Tamir <> | Subject | Re: [PATCH v6 net-next 1/5] net: add napi_id and hash |
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On 29/05/2013 23:09, Ben Hutchings wrote: > On Wed, 2013-05-29 at 09:39 +0300, Eliezer Tamir wrote: >> +void napi_hash_add(struct napi_struct *napi) >> +{ >> + if (!test_and_set_bit(NAPI_STATE_HASHED, &napi->state)) { >> + >> + spin_lock(&napi_hash_lock); >> + >> + /* 0 is not a valid id */ >> + napi->napi_id = 0; >> + while (!napi->napi_id) >> + napi->napi_id = ++napi_gen_id; > > Suppose we're loading/unloading one driver repeatedly while another one > remains loaded the whole time. Then once napi_gen_id wraps around, the > same ID can be assigned to multiple contexts. > > So far as I can see, assigning the same ID twice will just make polling > stop working for one of the NAPI contexts; I don't think it causes a > crash. And it is exceedingly unlikely to happen in production. But if > you're going to the trouble of handling wrap-around at all, you'd better > handle this.
OK
> [...] >> +/* must be called under rcu_read_lock(), as we dont take a reference */ >> +struct napi_struct *napi_by_id(int napi_id) >> +{ >> + unsigned int hash = napi_id % HASH_SIZE(napi_hash); > [...] > > napi_id should be declared unsigned int here, as elsewhere. The > division can't actually yield a negative result because HASH_SIZE() has > type size_t and napi_id is promoted to match, but I had to go and look > at hashtable.h to check that.
Good catch,
Thanks, Eliezer
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