On Tue, Jul 25, 2017 at 3:11 AM, Shawn Lin <shawn.lin@xxxxxxxxxxxxxx> wrote:
> commit 304419d8a7e ("mmc: core: Allocate per-request data using
> the block layer core") refactored mechanism of queue handling
> caused mmc_init_request() can be called just after mmc_cleanup_queue()
> caused null pointer dereference.
>
> commit bbdc74dc19e09a ("mmc: block: Prevent new req entering queue
> after its cleanup")tried to fix the problem. However it actually miss
> one corner case.
>
> We could still reproduce the issue mentioned with these steps:
> (1) insert a SD card and mount it
> (2) hotplug it, so it will leave md->usage still be counted
> (3) reboot the system which will sync data and umount the card
>
> [Unable to handle kernel NULL pointer dereference at virtual address
> 00000000
> [user pgtable: 4k pages, 48-bit VAs, pgd = ffff80007bab3000
> [[0000000000000000] *pgd=000000007a828003, *pud=0000000078dce003,
> *pmd=000000007aab6003, *pte=0000000000000000
> [Internal error: Oops: 96000007 [#1] PREEMPT SMP
> [Modules linked in:
> [CPU: 3 PID: 3507 Comm: umount Tainted: G W
> 4.13.0-rc1-next-20170720-00012-g9d9bf45 #33
> [Hardware name: Firefly-RK3399 Board (DT)
> [task: ffff80007a1de200 task.stack: ffff80007a01c000
> [PC is at mmc_init_request+0x14/0xc4
> [LR is at alloc_request_size+0x4c/0x74
> [pc : [<ffff0000087d7150>] lr : [<ffff000008378fe0>] pstate: 600001c5
> [sp : ffff80007a01f8f0
>
> ....
>
> [[<ffff0000087d7150>] mmc_init_request+0x14/0xc4
> [[<ffff000008378fe0>] alloc_request_size+0x4c/0x74
> [[<ffff00000817ac28>] mempool_create_node+0xb8/0x17c
> [[<ffff00000837aadc>] blk_init_rl+0x9c/0x120
> [[<ffff000008396580>] blkg_alloc+0x110/0x234
> [[<ffff000008396ac8>] blkg_create+0x424/0x468
> [[<ffff00000839877c>] blkg_lookup_create+0xd8/0x14c
> [[<ffff0000083796bc>] generic_make_request_checks+0x368/0x3b0
> [[<ffff00000837b050>] generic_make_request+0x1c/0x240
>
> So mmc_blk_put wouldn't calling blk_cleanup_queue which actually
> the QUEUE_FLAG_DYING and QUEUE_FLAG_BYPASS should stay. Block core
> expect blk_queue_bypass_{start, end} internally to bypass/drain the
> queue before actually dying the queue, so it didn't expose API to
> set the queue bypass. I think we should set QUEUE_FLAG_BYPASS whenever
> queue is removed, although the md->usage is still counted, as no dispatch
> queue could be found then.
>
> commit 304419d8a7e9 ("mmc: core: Allocate per-request data using the block layer core")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>
WOW good catch there Shawn!
Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
Ulf: please pick this up for fixes.
Yours,
Linus Walleij
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