> -----Original Message----- > From: Johannes Berg [mailto:johannes@xxxxxxxxxxxxxxxx] > Sent: Friday, June 11, 2021 4:14 AM > To: Steven Ting > Cc: linux-wireless@xxxxxxxxxxxxxxx > Subject: Re: Is the extra_tx_headroom guarenteed ? > > Hi, > > > We encountered a problem that we use the extra_tx_headroom to reserve the headroom > > which we put the txdesc in. > > > > Current workaround is that we check our needed headroom size by skb_headroom() > > in the driver layer. > > > > Is extra_tx_headroom in struct ieee80211_hw always guaranteed? > > It _should_ be, IMHO. Having the check in all the drivers would be > pointless. > > > The header file describes: > > * @extra_tx_headroom: headroom to reserve in each transmit skb > > * for use by the driver (e.g. for transmit headers.) > > > > But when the skb goes through the ieee80211_amsdu_realloc_pad(), it does not > > take care of the extra_tx_headroom, i.e. the original reserved headroom might be > > eaten. > > OK, so I guess that's a bug there. > > > Does the ieee80211_amsdu_realloc_pad() lacks some check for extra_tx_headroom > > or the extra_tx_headroom in mac80211 is not guaranteed? > > I would say it lacks the checks - want to send a patch? > > > Furthermore, for the packet that would not be aggregate in A-MSDU and ndev->needed_headroom > > is not guaranteed, in this case whether mac80211 layer still guarantee the extra_tx_headroom ? > > Yes, this case should be handled. > We prepare a patchset [1] to fix the bug mentioned in this mail. [1] https://lore.kernel.org/linux-wireless/20210816085128.10931-1-pkshih@xxxxxxxxxxx/T/#t -- Ping-Ke
