On Mon, 26 Nov 2018 14:25:44 +0100 Miquel Raynal miquel.raynal@bootlin.com wrote:
Hi Jagan,
Jagan Teki jagan@openedev.com wrote on Mon, 26 Nov 2018 18:35:01 +0530:
On 26/11/18 6:12 PM, Boris Brezillon wrote:
On Mon, 26 Nov 2018 13:37:46 +0100 Boris Brezillon boris.brezillon@bootlin.com wrote:
On Mon, 26 Nov 2018 16:42:48 +0530 Jagan Teki jagan@openedev.com wrote:
On 26/11/18 2:12 PM, Boris Brezillon wrote:
Hi Jagan,
On Thu, 22 Nov 2018 09:40:56 +0100 Boris Brezillon boris.brezillon@bootlin.com wrote: >>>>>>> + /* >>> + * Setting mtd->priv to NULL is the best we can do. Thanks to that, >>> + * the MTD layer can still call mtd hooks without risking a >>> + * use-after-free bug. Still, things should be fixed to prevent the >>> + * spi_flash object from being destroyed when del_mtd_device() fails. >>> + */ >>> + sf_mtd_info.priv = NULL; >>> + printf("Failed to unregister MTD %s and the spi_flash object is going away: you're in deep trouble!", >>> + sf_mtd_info.name); >> >> Why do we need this print? > > Yes we do, just to keep the user informed that something bad happened > and its spi-flash is no longer usable (at least through the MTD layer). > >>>>>> can't we do the same thing in MTD core >> itself, so-that it can be generic for all flash objects. > > del_mtd_device() can fail, so it's the caller responsibility to decide > what to do when that happens. Some users will propagate the error to > the upper layer and maybe cancel the device removal (AFAICT, > driver->remove() can return an error, not sure what happens in this > case though). For others, like spi-flash, the device will go away, and > all subsequent accesses will fail.
I'm about to send a new version fixing the problem I mentioned in patch 3, but before doing that, I'd like to know if my answer convinced you or if you'd still prefer this message to go away (or be placed in mtdcore/mtdpart.c).
I'm thinking of having the message still in MTD by showing which interface it would belongs, along with the details.
Then we'd need something less
Sorry, I inadvertently hit the send button :-/.
So, I was about to say that we need something less worrisome than the message I added in the SF layer if we move it to the MTD layer because some drivers might actually do the right thing when del_mtd_device() returns an error. I keep thinking that putting an error message in mtdcore.c is not the right thing to do, but if you insist, I'll add one (maybe a debug()). In any case I'd like to keep the one we have here, because in this specific case, there's simply nothing we can do when MTD dev removal fails.
Look like other flashes were deleting only via mtd_partitions. how would they know and does it not need for them to print the same information?
Do you see that sf does not use MTD in a consistent manner? The whole point of this commit is to handle sf's lightnesses in a "more robust" manner. This warning belongs to sf and not to the mtdcore, because as stated in the comment above, we should "prevent the spi_flash object from being destroyed when del_mtd_device() fails". If you don't want such warning in sf, I think the best thing to do is to fix the root issue.
Jagan, are you okay with this suggestion (add a debug() message in the del_mtd_device() path and keep the one we already have in sf_mtd.c)?