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    SubjectRe: [PATCH] media: vsp1: dl: Fix NULL pointer dereference on unbind
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    Hi Eugeniu,

    Yeouch. Looks like I really missed a trick there!

    We should probably update the $SUBJECT to match what is performed in the
    patch, which is perhaps more like:

    "media: vsp1: dl: Store VSP reference when creating cmd pools"

    On 23/05/2020 09:13, Eugeniu Rosca wrote:

    And then we can explain here:

    In commit f3b98e3c4d2e16 ("media: vsp1: Provide support for extended
    command pools"), the vsp pointer used for referencing the VSP1 device
    structure from a command pool during vsp1_dl_ext_cmd_pool_destroy() was
    not populated.

    Correctly assign the pointer to prevent the following
    null-pointer-dereference when removing the device:

    > v4.19 commit f3b98e3c4d2e16 ("media: vsp1: Provide support for extended
    > command pools") introduced below issue [*], consistently reproduced.
    >
    > In order to fix it, inspire from the sibling/predecessor v4.18-rc1
    > commit 5de0473982aab2 ("media: vsp1: Provide a body pool"), which saves
    > the vsp1 instance address in vsp1_dl_body_pool_create().
    >
    > [*] h3ulcb-kf #>
    > echo fea28000.vsp > /sys/bus/platform/devices/fea28000.vsp/driver/unbind
    > Unable to handle kernel NULL pointer dereference at virtual address 0000000000000028
    > Mem abort info:
    > ESR = 0x96000006
    > EC = 0x25: DABT (current EL), IL = 32 bits
    > SET = 0, FnV = 0
    > EA = 0, S1PTW = 0
    > Data abort info:
    > ISV = 0, ISS = 0x00000006
    > CM = 0, WnR = 0
    > user pgtable: 4k pages, 48-bit VAs, pgdp=00000007318be000
    > [0000000000000028] pgd=00000007333a1003, pud=00000007333a6003, pmd=0000000000000000
    > Internal error: Oops: 96000006 [#1] PREEMPT SMP
    > Modules linked in:
    > CPU: 1 PID: 486 Comm: sh Not tainted 5.7.0-rc6-arm64-renesas-00118-ge644645abf47 #185
    > Hardware name: Renesas H3ULCB Kingfisher board based on r8a77951 (DT)
    > pstate: 40000005 (nZcv daif -PAN -UAO)
    > pc : vsp1_dlm_destroy+0xe4/0x11c
    > lr : vsp1_dlm_destroy+0xc8/0x11c
    > sp : ffff800012963b60
    > x29: ffff800012963b60 x28: ffff0006f83fc440
    > x27: 0000000000000000 x26: ffff0006f5e13e80
    > x25: ffff0006f5e13ed0 x24: ffff0006f5e13ed0
    > x23: ffff0006f5e13ed0 x22: dead000000000122
    > x21: ffff0006f5e3a080 x20: ffff0006f5df2938
    > x19: ffff0006f5df2980 x18: 0000000000000003
    > x17: 0000000000000000 x16: 0000000000000016
    > x15: 0000000000000003 x14: 00000000000393c0
    > x13: ffff800011a5ec18 x12: ffff800011d8d000
    > x11: ffff0006f83fcc68 x10: ffff800011a53d70
    > x9 : ffff8000111f3000 x8 : 0000000000000000
    > x7 : 0000000000210d00 x6 : 0000000000000000
    > x5 : ffff800010872e60 x4 : 0000000000000004
    > x3 : 0000000078068000 x2 : ffff800012781000
    > x1 : 0000000000002c00 x0 : 0000000000000000
    > Call trace:
    > vsp1_dlm_destroy+0xe4/0x11c
    > vsp1_wpf_destroy+0x10/0x20
    > vsp1_entity_destroy+0x24/0x4c
    > vsp1_destroy_entities+0x54/0x130
    > vsp1_remove+0x1c/0x40
    > platform_drv_remove+0x28/0x50
    > __device_release_driver+0x178/0x220
    > device_driver_detach+0x44/0xc0
    > unbind_store+0xe0/0x104
    > drv_attr_store+0x20/0x30
    > sysfs_kf_write+0x48/0x70
    > kernfs_fop_write+0x148/0x230
    > __vfs_write+0x18/0x40
    > vfs_write+0xdc/0x1c4
    > ksys_write+0x68/0xf0
    > __arm64_sys_write+0x18/0x20
    > el0_svc_common.constprop.0+0x70/0x170
    > do_el0_svc+0x20/0x80
    > el0_sync_handler+0x134/0x1b0
    > el0_sync+0x140/0x180
    > Code: b40000c2 f9403a60 d2800084 a9400663 (f9401400)
    > ---[ end trace 3875369841fb288a ]---
    >
    > Fixes: f3b98e3c4d2e16 ("media: vsp1: Provide support for extended command pools")
    > Cc: stable@vger.kernel.org # v4.19+
    > Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>

    Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>

    > ---
    >
    > How about adding a new unit test perfoming unbind/rebind to
    > http://git.ideasonboard.com/renesas/vsp-tests.git, to avoid
    > such issues in future?

    Yes, now I wish I had done so back at 4.19! I hope this wasn't too
    painful to diagnose and fix, and thank you for being so thorough in your
    report!


    > Locally, below command has been used to identify the problem:
    >
    > for f in $(find /sys/bus/platform/devices/ -name "*vsp*" -o -name "*fdp*"); do \
    > b=$(basename $f); \
    > echo $b > $f/driver/unbind; \
    > done
    >

    I've created a test to add to vsp-tests, which I'll post next, thank you
    for the suggestion.

    Before your patch is applied, I experience the same crash you have seen,
    and after your patch - I can successfully unbind/bind all of the VSP1
    instances.

    So I think you can have this too:

    Tested-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>

    > ---
    > drivers/media/platform/vsp1/vsp1_dl.c | 2 ++
    > 1 file changed, 2 insertions(+)
    >
    > diff --git a/drivers/media/platform/vsp1/vsp1_dl.c b/drivers/media/platform/vsp1/vsp1_dl.c
    > index d7b43037e500..e07b135613eb 100644
    > --- a/drivers/media/platform/vsp1/vsp1_dl.c
    > +++ b/drivers/media/platform/vsp1/vsp1_dl.c
    > @@ -431,6 +431,8 @@ vsp1_dl_cmd_pool_create(struct vsp1_device *vsp1, enum vsp1_extcmd_type type,
    > if (!pool)
    > return NULL;
    >
    > + pool->vsp1 = vsp1;
    > +
    > spin_lock_init(&pool->lock);
    > INIT_LIST_HEAD(&pool->free);
    >
    >

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