Hi Kalle,
On Wed, Feb 06, 2019 at 05:41:43PM -0800, Brian Norris wrote:
> The DIAG copy engine is only used via polling, but it holds a spinlock
> with softirqs disabled. Each iteration of our read/write loops can
> theoretically take 20ms (two 10ms timeout loops), and this loop can be
> run an unbounded number of times while holding the spinlock -- dependent
> on the request size given by the caller.
>
> As of commit 39501ea64116 ("ath10k: download firmware via diag Copy
> Engine for QCA6174 and QCA9377."), we transfer large chunks of firmware
> memory using this mechanism. With large enough firmware segments, this
> becomes an exceedingly long period for disabling soft IRQs. For example,
> with a 500KiB firmware segment, in testing QCA6174A, I see 200 loop
> iterations of about 50-100us each, which can total about 10-20ms.
>
> In reality, we don't really need to block softirqs for this duration.
> The DIAG CE is only used in polling mode, and we only need to hold
> ce_lock to make sure any CE bookkeeping is done without screwing up
> another CE. Otherwise, we only need to ensure exclusion between
> ath10k_pci_diag_{read,write}_mem() contexts.
>
> This patch moves to use fine-grained locking for the shared ce_lock,
> while adding a new mutex just to ensure mutual exclusion of diag
> read/write operations.
>
> Tested on QCA6174A, firmware version WLAN.RM.4.4.1-00132-QCARMSWPZ-1.
>
> Fixes: 39501ea64116 ("ath10k: download firmware via diag Copy Engine for QCA6174 and QCA9377.")
> Signed-off-by: Brian Norris <briannorris@xxxxxxxxxxxx>
It would appear that this triggers new warnings
BUG: sleeping function called from invalid context
when handling firmware crashes. The call stack is
ath10k_pci_fw_crashed_dump
-> ath10k_pci_dump_memory
...
-> ath10k_pci_diag_read_mem
and the problem is that we're holding the 'data_lock' spinlock with
softirqs disabled, while later trying to grab this new mutex.
Unfortunately, data_lock is used in a lot of places, and it's unclear if
it can be migrated to a mutex as well. It seems like it probably can be,
but I'd have to audit a little more closely.
Any thoughts on what the short- and long-term solutions should be? I can
send a revert, to get v5.1 fixed. But it still seems like we should
avoid disabling softirqs for so long.
Brian
