Hi Roger, On Mon, 16 Oct 2017 13:22:04 +0300 Roger Quadros <rogerq@xxxxxx> wrote: > > Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki > > On 13/10/17 23:29, Boris Brezillon wrote: > > On Fri, 13 Oct 2017 22:24:58 +0200 > > Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx> wrote: > > > >> On Fri, 13 Oct 2017 14:50:33 +0200 > >> Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx> wrote: > >> > >>> On Fri, 13 Oct 2017 14:57:29 +0300 > >>> Roger Quadros <rogerq@xxxxxx> wrote: > >>> > >>>> Hi Boris, > >>>> > >>>> NAND on gpmc-omap breaks for me while doing a unmount of a ubi volume since v4.12 > >>>> > >>>> Behaviour follows through in v4.13 and v4.14-rc as well. > >>>> > >>>> Do you have any idea about this? > >> > >> More info on what has changed in 4.12: we no longer allocate the > >> nand_buffer struct + its internal buffer using a single big kmalloc > >> call, which means the nand_buffer struct is now likely to be allocated > >> in a small object slab (sizeof(nand_buffers) = 12). If you have a > >> use-after-free bug somewhere in the kernel, it might corrupt the > > Spot on. Problem starts from commit 4d5dea5725f3aa95b9b64e252540e435dd216dbc > "mtd: nand: allocate aligned buffers if NAND_OWN_BUFFERS is unset" > > > > > I meant buffer-overflow, not use-after-free. > > Your analysis seems correct. > > > > >> nand_buffers object, which might explain the bug you see here. > >> > >>> > >>> Can you try with this patch [1] applied and paste me the values printed > >>> just before the crash? > >>> > >>> [1]http://code.bulix.org/lc8xk0-209746 > > == unmounting volume > [ 36.308792] nand: nand_write_subpage_hwecc:2575 ecc_calc = (null) oob_poi = ed096800 > [ 36.317319] mtd_ooblayout_set_bytes:1330 dst = ed096802 src = (null) > [ 36.324162] Unable to handle kernel NULL pointer dereference at virtual address 00000000 > > > Running the following patch > https://hastebin.com/ulogurutuz.php > shows > > [ 37.260689] nand: nand_write_subpage_hwecc:2547:A ecc_calc = ed116e40 oob_poi = ed117800 > [ 37.260772] nand: nand_write_subpage_hwecc:2556:A1:step 0, ecc_calc = ed116e40 > [ 37.260779] nand: nand_write_subpage_hwecc:2562:A2:step 0, ecc_calc = ed116e40 > [ 37.260834] nand: nand_write_subpage_hwecc:2556:A1:step 1, ecc_calc = ed116e40 > [ 37.260840] nand: nand_write_subpage_hwecc:2567:A3-pre:step 1, ecc_calc = ed116e40 > [ 37.260846] omap_calculate_ecc_bch > [ 37.260856] nand: nand_write_subpage_hwecc:2570:A3-post:step 1, ecc_calc = (null) > [ 37.260912] nand: nand_write_subpage_hwecc:2556:A1:step 2, ecc_calc = (null) > [ 37.260918] nand: nand_write_subpage_hwecc:2562:A2:step 2, ecc_calc = (null) > [ 37.260972] nand: nand_write_subpage_hwecc:2556:A1:step 3, ecc_calc = (null) > [ 37.260978] nand: nand_write_subpage_hwecc:2562:A2:step 3, ecc_calc = (null) > [ 37.260984] nand: nand_write_subpage_hwecc:2587:B ecc_calc = (null) oob_poi = ed117800 > [ 37.260991] mtd_ooblayout_set_bytes:1330 dst = ed117802 src = (null) > > which means omap_calculate_ecc_bch() it the culprit. > > Looks like the function calculates and stores ECC for all sectors even if we just want ECC > for just one sector (sub-page). Yes, looks like you find the root cause. > > Is my understanding correct > - We should not be hooking the multi-sector ECC calculator omap_calculate_ecc_bch() to ecc.calculate > - provide a new one sector ECC calculator function (for BCH4/8/16) for omap and hook it to ecc.calculate > OR > - override nand_read_subpage() and nand_write_subpage() using omap specific implementation (for BCH4/8/16). Second solution sounds simpler because the ECC sector information is not passed to ecc->calculate() hook, which means you'd have to extract it from the ecc_calc pointer: (uintptr_t)(ecc_calc - chip->buffers->ecccalc) / chip->ecc.size and doing arithmetic on pointers is usually not a good idea. Anyway, I'd be fine with both solutions, so pick the one you prefer. Regards, Boris -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
