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SubjectRe: [PATCH 0/3] mtd: core: protect access to mtd devices while in suspend
On Wed, 20 Oct 2021 09:23:52 +0200
Sean Nyekjaer <sean@geanix.com> wrote:

> On Wed, Oct 20, 2021 at 09:12:28AM +0200, Miquel Raynal wrote:
> > >
> > > Actually, this version is even cleaner:
> > >
> > > diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> > > index 3d6c6e880520..98c39b7f6279 100644
> > > --- a/drivers/mtd/nand/raw/nand_base.c
> > > +++ b/drivers/mtd/nand/raw/nand_base.c
> > > @@ -6222,8 +6222,6 @@ static int nand_scan_tail(struct nand_chip *chip)
> > > mtd->_sync = nand_sync;
> > > mtd->_lock = nand_lock;
> > > mtd->_unlock = nand_unlock;
> > > - mtd->_suspend = nand_suspend;
> > > - mtd->_resume = nand_resume;
> > > mtd->_reboot = nand_shutdown;
> > > mtd->_block_isreserved = nand_block_isreserved;
> > > mtd->_block_isbad = nand_block_isbad;
> > > @@ -6261,14 +6259,20 @@ static int nand_scan_tail(struct nand_chip *chip)
> > > goto err_free_interface_config;
> > >
> > > /* Check, if we should skip the bad block table scan */
> > > - if (chip->options & NAND_SKIP_BBTSCAN)
> > > - return 0;
> > > -
> > > - /* Build bad block table */
> > > - ret = nand_create_bbt(chip);
> > > - if (ret)
> > > - goto err_free_secure_regions;
> > > + if (chip->options & NAND_SKIP_BBTSCAN) {
> > > + /* Build bad block table */
> > > + ret = nand_create_bbt(chip);
> > > + if (ret)
> > > + goto err_free_secure_regions;
> > > + }
> >
> > Nice idea.
> >
> > >
> > > + /*
> > > + * Populate the suspend/resume hooks after the BBT has been scanned to
> > > + * avoid using the suspend lock and resume waitqueue which are only
> > > + * initialized when mtd_device_register() is called.
> > > + */
> > > + mtd->_suspend = nand_suspend;
> > > + mtd->_resume = nand_resume;
> > > return 0;
> > >
> > > err_free_secure_regions:
>
> Could be a nice idea, but it doesn't work...
> gpmi-nand.c calls nand_create_bbt() after this have run ;)

Er, indeed. Can you try with this instead:

diff --git a/drivers/mtd/nand/raw/nand_bbt.c b/drivers/mtd/nand/raw/nand_bbt.c
index b7ad030225f8..548647bd27a4 100644
--- a/drivers/mtd/nand/raw/nand_bbt.c
+++ b/drivers/mtd/nand/raw/nand_bbt.c
@@ -1397,8 +1397,28 @@ static int nand_create_badblock_pattern(struct nand_chip *this)
*/
int nand_create_bbt(struct nand_chip *this)
{
+ struct mtd_info *mtd = nand_to_mtd(this)
+ int (*suspend) (struct mtd_info *) = mtd->_suspend;
+ int (*resume) (struct mtd_info *) = mtd->_resume;
int ret;

+ /*
+ * The BBT scan logic use the MTD helpers before the MTD layer had a
+ * chance to initialize the device, and that leads to issues when
+ * accessing the uninitialized suspend lock. Let's temporarily set the
+ * suspend/resume hooks to NULL to skip the lock acquire/release step.
+ *
+ * FIXME: This is an ugly hack, so please don't copy this pattern to
+ * other MTD implementations. The proper fix would be to implement a
+ * generic BBT scan logic at the NAND level that's not using any of the
+ * MTD helpers to access pages. We also might consider doing a two
+ * step initialization at the MTD level (mtd_device_init() +
+ * mtd_device_register()) so some of the fields are initialized
+ * early.
+ */
+ mtd->_suspend = NULL;
+ mtd->_resume = NULL;
+
/* Is a flash based bad block table requested? */
if (this->bbt_options & NAND_BBT_USE_FLASH) {
/* Use the default pattern descriptors */
@@ -1422,7 +1442,13 @@ int nand_create_bbt(struct nand_chip *this)
return ret;
}

- return nand_scan_bbt(this, this->badblock_pattern);
+ ret = nand_scan_bbt(this, this->badblock_pattern);
+
+ /* Restore the suspend/resume hooks. */
+ mtd->_suspend = suspend;
+ mtd->_resume = resume;
+
+ return ret;
}
EXPORT_SYMBOL(nand_create_bbt);

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