[PATCH AUTOSEL 4.14 1/6] ata/libata: Fix usage of page address by page_address in ata_scsi_mode_select_xlat function

[PATCH AUTOSEL 4.14 1/6] ata/libata: Fix usage of page address by page_address in ata_scsi_mode_select_xlat function

[Sasha Levin]

From: Ye Bin <yebin10@huawei.com>

[ Upstream commit f650ef61e040bcb175dd8762164b00a5d627f20e ]

BUG: KASAN: use-after-free in ata_scsi_mode_select_xlat+0x10bd/0x10f0
drivers/ata/libata-scsi.c:4045
Read of size 1 at addr ffff88803b8cd003 by task syz-executor.6/12621

CPU: 1 PID: 12621 Comm: syz-executor.6 Not tainted 4.19.95 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.10.2-1ubuntu1 04/01/2014
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0xac/0xee lib/dump_stack.c:118
print_address_description+0x60/0x223 mm/kasan/report.c:253
kasan_report_error mm/kasan/report.c:351 [inline]
kasan_report mm/kasan/report.c:409 [inline]
kasan_report.cold+0xae/0x2d8 mm/kasan/report.c:393
ata_scsi_mode_select_xlat+0x10bd/0x10f0 drivers/ata/libata-scsi.c:4045
ata_scsi_translate+0x2da/0x680 drivers/ata/libata-scsi.c:2035
__ata_scsi_queuecmd drivers/ata/libata-scsi.c:4360 [inline]
ata_scsi_queuecmd+0x2e4/0x790 drivers/ata/libata-scsi.c:4409
scsi_dispatch_cmd+0x2ee/0x6c0 drivers/scsi/scsi_lib.c:1867
scsi_queue_rq+0xfd7/0x1990 drivers/scsi/scsi_lib.c:2170
blk_mq_dispatch_rq_list+0x1e1/0x19a0 block/blk-mq.c:1186
blk_mq_do_dispatch_sched+0x147/0x3d0 block/blk-mq-sched.c:108
blk_mq_sched_dispatch_requests+0x427/0x680 block/blk-mq-sched.c:204
__blk_mq_run_hw_queue+0xbc/0x200 block/blk-mq.c:1308
__blk_mq_delay_run_hw_queue+0x3c0/0x460 block/blk-mq.c:1376
blk_mq_run_hw_queue+0x152/0x310 block/blk-mq.c:1413
blk_mq_sched_insert_request+0x337/0x6c0 block/blk-mq-sched.c:397
blk_execute_rq_nowait+0x124/0x320 block/blk-exec.c:64
blk_execute_rq+0xc5/0x112 block/blk-exec.c:101
sg_scsi_ioctl+0x3b0/0x6a0 block/scsi_ioctl.c:507
sg_ioctl+0xd37/0x23f0 drivers/scsi/sg.c:1106
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:501 [inline]
do_vfs_ioctl+0xae6/0x1030 fs/ioctl.c:688
ksys_ioctl+0x76/0xa0 fs/ioctl.c:705
__do_sys_ioctl fs/ioctl.c:712 [inline]
__se_sys_ioctl fs/ioctl.c:710 [inline]
__x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:710
do_syscall_64+0xa0/0x2e0 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45c479
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89
f7 48
89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f
83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fb0e9602c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fb0e96036d4 RCX: 000000000045c479
RDX: 0000000020000040 RSI: 0000000000000001 RDI: 0000000000000003
RBP: 000000000076bfc0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 000000000000046d R14: 00000000004c6e1a R15: 000000000076bfcc

Allocated by task 12577:
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc mm/kasan/kasan.c:553 [inline]
kasan_kmalloc+0xbf/0xe0 mm/kasan/kasan.c:531
__kmalloc+0xf3/0x1e0 mm/slub.c:3749
kmalloc include/linux/slab.h:520 [inline]
load_elf_phdrs+0x118/0x1b0 fs/binfmt_elf.c:441
load_elf_binary+0x2de/0x4610 fs/binfmt_elf.c:737
search_binary_handler fs/exec.c:1654 [inline]
search_binary_handler+0x15c/0x4e0 fs/exec.c:1632
exec_binprm fs/exec.c:1696 [inline]
__do_execve_file.isra.0+0xf52/0x1a90 fs/exec.c:1820
do_execveat_common fs/exec.c:1866 [inline]
do_execve fs/exec.c:1883 [inline]
__do_sys_execve fs/exec.c:1964 [inline]
__se_sys_execve fs/exec.c:1959 [inline]
__x64_sys_execve+0x8a/0xb0 fs/exec.c:1959
do_syscall_64+0xa0/0x2e0 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Freed by task 12577:
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x129/0x170 mm/kasan/kasan.c:521
slab_free_hook mm/slub.c:1370 [inline]
slab_free_freelist_hook mm/slub.c:1397 [inline]
slab_free mm/slub.c:2952 [inline]
kfree+0x8b/0x1a0 mm/slub.c:3904
load_elf_binary+0x1be7/0x4610 fs/binfmt_elf.c:1118
search_binary_handler fs/exec.c:1654 [inline]
search_binary_handler+0x15c/0x4e0 fs/exec.c:1632
exec_binprm fs/exec.c:1696 [inline]
__do_execve_file.isra.0+0xf52/0x1a90 fs/exec.c:1820
do_execveat_common fs/exec.c:1866 [inline]
do_execve fs/exec.c:1883 [inline]
__do_sys_execve fs/exec.c:1964 [inline]
__se_sys_execve fs/exec.c:1959 [inline]
__x64_sys_execve+0x8a/0xb0 fs/exec.c:1959
do_syscall_64+0xa0/0x2e0 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x44/0xa9

The buggy address belongs to the object at ffff88803b8ccf00
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 259 bytes inside of
512-byte region [ffff88803b8ccf00, ffff88803b8cd100)
The buggy address belongs to the page:
page:ffffea0000ee3300 count:1 mapcount:0 mapping:ffff88806cc03080
index:0xffff88803b8cc780 compound_mapcount: 0
flags: 0x100000000008100(slab|head)
raw: 0100000000008100 ffffea0001104080 0000000200000002 ffff88806cc03080
raw: ffff88803b8cc780 00000000800c000b 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88803b8ccf00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88803b8ccf80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88803b8cd000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88803b8cd080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88803b8cd100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

You can refer to "https://www.lkml.org/lkml/2019/1/17/474" reproduce
this error.

The exception code is "bd_len = p[3];", "p" value is ffff88803b8cd000
which belongs to the cache kmalloc-512 of size 512. The "page_address(sg_page(scsi_sglist(scmd)))"
maybe from sg_scsi_ioctl function "buffer" which allocated by kzalloc, so "buffer"
may not page aligned.
This also looks completely buggy on highmem systems and really needs to use a
kmap_atomic.      --Christoph Hellwig
To address above bugs, Paolo Bonzini advise to simpler to just make a char array
of size CACHE_MPAGE_LEN+8+8+4-2(or just 64 to make it easy), use sg_copy_to_buffer
to copy from the sglist into the buffer, and workthere.

Signed-off-by: Ye Bin <yebin10@huawei.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/ata/libata-scsi.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 2f81d65342709..bc2c27f0493fc 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -3996,12 +3996,13 @@ static unsigned int ata_scsi_mode_select_xlat(struct ata_queued_cmd *qc)
 {
 	struct scsi_cmnd *scmd = qc->scsicmd;
 	const u8 *cdb = scmd->cmnd;
-	const u8 *p;
 	u8 pg, spg;
 	unsigned six_byte, pg_len, hdr_len, bd_len;
 	int len;
 	u16 fp = (u16)-1;
 	u8 bp = 0xff;
+	u8 buffer[64];
+	const u8 *p = buffer;
 
 	VPRINTK("ENTER\n");
 
@@ -4035,12 +4036,14 @@ static unsigned int ata_scsi_mode_select_xlat(struct ata_queued_cmd *qc)
 	if (!scsi_sg_count(scmd) || scsi_sglist(scmd)->length < len)
 		goto invalid_param_len;
 
-	p = page_address(sg_page(scsi_sglist(scmd)));
-
 	/* Move past header and block descriptors.  */
 	if (len < hdr_len)
 		goto invalid_param_len;
 
+	if (!sg_copy_to_buffer(scsi_sglist(scmd), scsi_sg_count(scmd),
+			       buffer, sizeof(buffer)))
+		goto invalid_param_len;
+
 	if (six_byte)
 		bd_len = p[3];
 	else
-- 
2.25.1

[PATCH AUTOSEL 4.14 2/6] net: alx: fix race condition in alx_remove

[Sasha Levin]

From: Zekun Shen <bruceshenzk@gmail.com>

[ Upstream commit e89df5c4322c1bf495f62d74745895b5fd2a4393 ]

There is a race condition exist during termination. The path is
alx_stop and then alx_remove. An alx_schedule_link_check could be called
before alx_stop by interrupt handler and invoke alx_link_check later.
Alx_stop frees the napis, and alx_remove cancels any pending works.
If any of the work is scheduled before termination and invoked before
alx_remove, a null-ptr-deref occurs because both expect alx->napis[i].

This patch fix the race condition by moving cancel_work_sync functions
before alx_free_napis inside alx_stop. Because interrupt handler can call
alx_schedule_link_check again, alx_free_irq is moved before
cancel_work_sync calls too.

Signed-off-by: Zekun Shen <bruceshenzk@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/net/ethernet/atheros/alx/main.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/atheros/alx/main.c b/drivers/net/ethernet/atheros/alx/main.c
index 5e5022fa1d047..85029d43da758 100644
--- a/drivers/net/ethernet/atheros/alx/main.c
+++ b/drivers/net/ethernet/atheros/alx/main.c
@@ -1250,8 +1250,12 @@ static int __alx_open(struct alx_priv *alx, bool resume)
 
 static void __alx_stop(struct alx_priv *alx)
 {
-	alx_halt(alx);
 	alx_free_irq(alx);
+
+	cancel_work_sync(&alx->link_check_wk);
+	cancel_work_sync(&alx->reset_wk);
+
+	alx_halt(alx);
 	alx_free_rings(alx);
 	alx_free_napis(alx);
 }
@@ -1863,9 +1867,6 @@ static void alx_remove(struct pci_dev *pdev)
 	struct alx_priv *alx = pci_get_drvdata(pdev);
 	struct alx_hw *hw = &alx->hw;
 
-	cancel_work_sync(&alx->link_check_wk);
-	cancel_work_sync(&alx->reset_wk);
-
 	/* restore permanent mac address */
 	alx_set_macaddr(hw, hw->perm_addr);
 
-- 
2.25.1

[PATCH AUTOSEL 4.14 3/6] rocker: fix incorrect error handling in dma_rings_init

[Sasha Levin]

From: Aditya Pakki <pakki001@umn.edu>

[ Upstream commit 58d0c864e1a759a15c9df78f50ea5a5c32b3989e ]

In rocker_dma_rings_init, the goto blocks in case of errors
caused by the functions rocker_dma_cmd_ring_waits_alloc() and
rocker_dma_ring_create() are incorrect. The patch fixes the
order consistent with cleanup in rocker_dma_rings_fini().

Signed-off-by: Aditya Pakki <pakki001@umn.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/net/ethernet/rocker/rocker_main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/rocker/rocker_main.c b/drivers/net/ethernet/rocker/rocker_main.c
index 056cb60936303..8ad05e5008299 100644
--- a/drivers/net/ethernet/rocker/rocker_main.c
+++ b/drivers/net/ethernet/rocker/rocker_main.c
@@ -651,10 +651,10 @@ static int rocker_dma_rings_init(struct rocker *rocker)
 err_dma_event_ring_bufs_alloc:
 	rocker_dma_ring_destroy(rocker, &rocker->event_ring);
 err_dma_event_ring_create:
+	rocker_dma_cmd_ring_waits_free(rocker);
+err_dma_cmd_ring_waits_alloc:
 	rocker_dma_ring_bufs_free(rocker, &rocker->cmd_ring,
 				  PCI_DMA_BIDIRECTIONAL);
-err_dma_cmd_ring_waits_alloc:
-	rocker_dma_cmd_ring_waits_free(rocker);
 err_dma_cmd_ring_bufs_alloc:
 	rocker_dma_ring_destroy(rocker, &rocker->cmd_ring);
 	return err;
-- 
2.25.1

[PATCH AUTOSEL 4.14 4/6] s390/ptrace: fix setting syscall number

[Sasha Levin]

From: Sven Schnelle <svens@linux.ibm.com>

[ Upstream commit 873e5a763d604c32988c4a78913a8dab3862d2f9 ]

When strace wants to update the syscall number, it sets GPR2
to the desired number and updates the GPR via PTRACE_SETREGSET.
It doesn't update regs->int_code which would cause the old syscall
executed on syscall restart. As we cannot change the ptrace ABI and
don't have a field for the interruption code, check whether the tracee
is in a syscall and the last instruction was svc. In that case assume
that the tracer wants to update the syscall number and copy the GPR2
value to regs->int_code.

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/s390/kernel/ptrace.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/arch/s390/kernel/ptrace.c b/arch/s390/kernel/ptrace.c
index 56e0190d6e651..42e4cd20fbbed 100644
--- a/arch/s390/kernel/ptrace.c
+++ b/arch/s390/kernel/ptrace.c
@@ -322,6 +322,25 @@ static inline void __poke_user_per(struct task_struct *child,
 		child->thread.per_user.end = data;
 }
 
+static void fixup_int_code(struct task_struct *child, addr_t data)
+{
+	struct pt_regs *regs = task_pt_regs(child);
+	int ilc = regs->int_code >> 16;
+	u16 insn;
+
+	if (ilc > 6)
+		return;
+
+	if (ptrace_access_vm(child, regs->psw.addr - (regs->int_code >> 16),
+			&insn, sizeof(insn), FOLL_FORCE) != sizeof(insn))
+		return;
+
+	/* double check that tracee stopped on svc instruction */
+	if ((insn >> 8) != 0xa)
+		return;
+
+	regs->int_code = 0x20000 | (data & 0xffff);
+}
 /*
  * Write a word to the user area of a process at location addr. This
  * operation does have an additional problem compared to peek_user.
@@ -333,7 +352,9 @@ static int __poke_user(struct task_struct *child, addr_t addr, addr_t data)
 	struct user *dummy = NULL;
 	addr_t offset;
 
+
 	if (addr < (addr_t) &dummy->regs.acrs) {
+		struct pt_regs *regs = task_pt_regs(child);
 		/*
 		 * psw and gprs are stored on the stack
 		 */
@@ -351,7 +372,11 @@ static int __poke_user(struct task_struct *child, addr_t addr, addr_t data)
 				/* Invalid addressing mode bits */
 				return -EINVAL;
 		}
-		*(addr_t *)((addr_t) &task_pt_regs(child)->psw + addr) = data;
+
+		if (test_pt_regs_flag(regs, PIF_SYSCALL) &&
+			addr == offsetof(struct user, regs.gprs[2]))
+			fixup_int_code(child, data);
+		*(addr_t *)((addr_t) &regs->psw + addr) = data;
 
 	} else if (addr < (addr_t) (&dummy->regs.orig_gpr2)) {
 		/*
@@ -717,6 +742,10 @@ static int __poke_user_compat(struct task_struct *child,
 			regs->psw.mask = (regs->psw.mask & ~PSW_MASK_BA) |
 				(__u64)(tmp & PSW32_ADDR_AMODE);
 		} else {
+
+			if (test_pt_regs_flag(regs, PIF_SYSCALL) &&
+				addr == offsetof(struct compat_user, regs.gprs[2]))
+				fixup_int_code(child, data);
 			/* gpr 0-15 */
 			*(__u32*)((addr_t) &regs->psw + addr*2 + 4) = tmp;
 		}
-- 
2.25.1

[PATCH AUTOSEL 4.14 5/6] kbuild: improve cc-option to clean up all temporary files

[Sasha Levin]

From: Masahiro Yamada <masahiroy@kernel.org>

[ Upstream commit f2f02ebd8f3833626642688b2d2c6a7b3c141fa9 ]

When cc-option and friends evaluate compiler flags, the temporary file
$$TMP is created as an output object, and automatically cleaned up.
The actual file path of $$TMP is .<pid>.tmp, here <pid> is the process
ID of $(shell ...) invoked from cc-option. (Please note $$$$ is the
escape sequence of $$).

Such garbage files are cleaned up in most cases, but some compiler flags
create additional output files.

For example, -gsplit-dwarf creates a .dwo file.

When CONFIG_DEBUG_INFO_SPLIT=y, you will see a bunch of .<pid>.dwo files
left in the top of build directories. You may not notice them unless you
do 'ls -a', but the garbage files will increase every time you run 'make'.

This commit changes the temporary object path to .tmp_<pid>/tmp, and
removes .tmp_<pid> directory when exiting. Separate build artifacts such
as *.dwo will be cleaned up all together because their file paths are
usually determined based on the base name of the object.

Another example is -ftest-coverage, which outputs the coverage data into
<base-name-of-object>.gcno

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 scripts/Kbuild.include | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index a33fa1a918731..28bfb4378dbd8 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -82,20 +82,21 @@ cc-cross-prefix =  \
 		fi)))
 
 # output directory for tests below
-TMPOUT := $(if $(KBUILD_EXTMOD),$(firstword $(KBUILD_EXTMOD))/)
+TMPOUT = $(if $(KBUILD_EXTMOD),$(firstword $(KBUILD_EXTMOD))/).tmp_$$$$
 
 # try-run
 # Usage: option = $(call try-run, $(CC)...-o "$$TMP",option-ok,otherwise)
 # Exit code chooses option. "$$TMP" serves as a temporary file and is
 # automatically cleaned up.
 try-run = $(shell set -e;		\
-	TMP="$(TMPOUT).$$$$.tmp";	\
-	TMPO="$(TMPOUT).$$$$.o";	\
+	TMP=$(TMPOUT)/tmp;		\
+	TMPO=$(TMPOUT)/tmp.o;		\
+	mkdir -p $(TMPOUT);		\
+	trap "rm -rf $(TMPOUT)" EXIT;	\
 	if ($(1)) >/dev/null 2>&1;	\
 	then echo "$(2)";		\
 	else echo "$(3)";		\
-	fi;				\
-	rm -f "$$TMP" "$$TMPO")
+	fi)
 
 # as-option
 # Usage: cflags-y += $(call as-option,-Wa$(comma)-isa=foo,)
-- 
2.25.1

[PATCH AUTOSEL 4.14 6/6] blktrace: break out of blktrace setup on concurrent calls

[Sasha Levin]

From: Luis Chamberlain <mcgrof@kernel.org>

[ Upstream commit 1b0b283648163dae2a214ca28ed5a99f62a77319 ]

We use one blktrace per request_queue, that means one per the entire
disk.  So we cannot run one blktrace on say /dev/vda and then /dev/vda1,
or just two calls on /dev/vda.

We check for concurrent setup only at the very end of the blktrace setup though.

If we try to run two concurrent blktraces on the same block device the
second one will fail, and the first one seems to go on. However when
one tries to kill the first one one will see things like this:

The kernel will show these:

```
debugfs: File 'dropped' in directory 'nvme1n1' already present!
debugfs: File 'msg' in directory 'nvme1n1' already present!
debugfs: File 'trace0' in directory 'nvme1n1' already present!
``

And userspace just sees this error message for the second call:

```
blktrace /dev/nvme1n1
BLKTRACESETUP(2) /dev/nvme1n1 failed: 5/Input/output error
```

The first userspace process #1 will also claim that the files
were taken underneath their nose as well. The files are taken
away form the first process given that when the second blktrace
fails, it will follow up with a BLKTRACESTOP and BLKTRACETEARDOWN.
This means that even if go-happy process #1 is waiting for blktrace
data, we *have* been asked to take teardown the blktrace.

This can easily be reproduced with break-blktrace [0] run_0005.sh test.

Just break out early if we know we're already going to fail, this will
prevent trying to create the files all over again, which we know still
exist.

[0] https://github.com/mcgrof/break-blktrace

Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/trace/blktrace.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index a60c09e0bda87..52389be36f00f 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -15,6 +15,9 @@
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  *
  */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
 #include <linux/kernel.h>
 #include <linux/blkdev.h>
 #include <linux/blktrace_api.h>
@@ -504,6 +507,16 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
 	 */
 	strreplace(buts->name, '/', '_');
 
+	/*
+	 * bdev can be NULL, as with scsi-generic, this is a helpful as
+	 * we can be.
+	 */
+	if (q->blk_trace) {
+		pr_warn("Concurrent blktraces are not allowed on %s\n",
+			buts->name);
+		return -EBUSY;
+	}
+
 	bt = kzalloc(sizeof(*bt), GFP_KERNEL);
 	if (!bt)
 		return -ENOMEM;
-- 
2.25.1