Le 11/11/2021 à 10:17, Dan Carpenter a écrit :
On Wed, Nov 10, 2021 at 10:11:34PM +0100, Christophe JAILLET wrote:
In case of memory allocation failure, we should release many things and
should not return directly.
The tricky part here, is that some (kzalloc + dma_pool_alloc) resources
are allocated and stored in 'unusable' and a 'good' list.
The 'good' list is then freed and only the 'unusable' list remains
allocated.
So, only this 'unusable' list is then freed in the error handling path of
the function.
So, instead of adding even more code in this already huge function, just
'continue' (as already done if dma_pool_alloc() fails) instead of
returning directly.
After the 'for' loop, we will then branch to the correct place of the
error handling path when another memory allocation will (likely) fail
afterward.
Fixes: 50b812755e97 ("scsi: qla2xxx: Fix DMA error when the DIF sg buffer crosses 4GB boundary")
Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
---
Certainly not the best solution, but look 'safe' to me.
Your analysis seems correct, but this is deeply weird.
I agree, deeply weird :)
It sort of looks
like this was debug code that was committed accidentally. Neither
the "good" list nor the "unusable" are used except to print some debug
info:
ql_dbg_pci(ql_dbg_init, ha->pdev, 0x0024,
"%s: dif dma pool (good=%u unusable=%u)\n",
__func__, ha->pool.good.count,
ha->pool.unusable.count);
The good list is freed immediately, and then there is a no-op free in
qla2x00_mem_free().
I agree.
The unusable list is preserved until qla2x00_mem_free()
but not used anywhere.
I agree.
The logic in commit '50b812755e97' puzzled me a lot.
I wonder why the 128 magic number in the for loop.
My understanding is:
- try to allocate things at start-up
- check if this allocation crosses the 4G limit (see commit log)
- keep the "unusable" allocation allocated, so that this memory is
reserved (i.e. wasted) and won't be allocated later (see usage of the
dif_bundl_pool dma pool in [1])
- hope that tying 128 allocations is enough and that no "unusable
allocation" will be done at run-time.
In other words, I tried to convinced myself that there was a real logic,
even if unperfect.
Even if the above description is correct and if it works as expected in
RL, it real looks like an overkill!
Now that I reread code around 'dif_local_dma_alloc' usage, I'm tempt to
agree with your feeling about debug code.
CJ
[1]:
https://elixir.bootlin.com/linux/v5.15.1/source/drivers/scsi/qla2xxx/qla_iocb.c#L1138
regards,
dan carpenter
