[PATCH] mtd: partitions: Handle add_mtd_device() failures gracefully

[Geert Uytterhoeven <geert+renesas@glider.be>]

Currently add_mtd_device() failures are plainly ignored, which may lead
to kernel crashes later.

E.g. after flipping SW17 on r8a7791/koelsch, to switch from the large to
the small QSPI FLASH, without updating the partition description in DT,
the following happens:

    m25p80 spi0.0: found s25sl032p, expected s25fl512s
    3 fixed-partitions partitions found on MTD device spi0.0
    Creating 3 MTD partitions on "spi0.0":
    0x000000000000-0x000000080000 : "loader"
    0x000000080000-0x000000600000 : "user"
    mtd: partition "user" extends beyond the end of device "spi0.0" -- size truncated to 0x380000

The second partition is truncated correctly.

    0x000000600000-0x000004000000 : "flash"
    mtd: partition "flash" is out of reach -- disabled

The third partition is disabled by allocate_partition(), which means
fields like erasesize are not filled in.  Hence add_mtd_device() fails
and screams, rightfully:

    ------------[ cut here ]------------
    WARNING: CPU: 1 PID: 1 at drivers/mtd/mtdcore.c:508 add_mtd_device+0x2a0/0x2e0
    Modules linked in:
    CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.16.0-koelsch-08649-g58e35e77b00c075d #4029
    Hardware name: Generic R-Car Gen2 (Flattened Device Tree)
    [<c020f660>] (unwind_backtrace) from [<c020b2f4>] (show_stack+0x10/0x14)
    [<c020b2f4>] (show_stack) from [<c076d088>] (dump_stack+0x7c/0x9c)
    [<c076d088>] (dump_stack) from [<c02210d8>] (__warn+0xd4/0x104)
    [<c02210d8>] (__warn) from [<c0221218>] (warn_slowpath_null+0x38/0x44)
    [<c0221218>] (warn_slowpath_null) from [<c0553db4>] (add_mtd_device+0x2a0/0x2e0)
    [<c0553db4>] (add_mtd_device) from [<c0556a70>] (add_mtd_partitions+0xd0/0x16c)
    [<c0556a70>] (add_mtd_partitions) from [<c0553f88>] (mtd_device_parse_register+0xc4/0x1b4)
    [<c0553f88>] (mtd_device_parse_register) from [<c055a97c>] (m25p_probe+0x148/0x188)
    [<c055a97c>] (m25p_probe) from [<c055e278>] (spi_drv_probe+0x84/0xa0)

    [...]

    ---[ end trace d43ce221bca7ab5c ]---

However, that failure is ignored by add_mtd_partitions(), leading to a
crash later:

    ------------[ cut here ]------------
    kernel BUG at fs/sysfs/file.c:330!
    Internal error: Oops - BUG: 0 [#1] SMP ARM
    Modules linked in:
    CPU: 1 PID: 1 Comm: swapper/0 Tainted: G        W        4.16.0-koelsch-08649-g58e35e77b00c075d #4029
    Hardware name: Generic R-Car Gen2 (Flattened Device Tree)
    PC is at sysfs_create_file_ns+0x24/0x40
    LR is at 0x1
    pc : [<c03604cc>]    lr : [<00000001>]    psr: 60000013
    sp : eb447c00  ip : 00000000  fp : c0e20174
    r10: 00000003  r9 : c0e20150  r8 : eb7e3818
    r7 : ea8b20f8  r6 : c0e2017c  r5 : 00000000  r4 : 00000000
    r3 : 00000200  r2 : 00000000  r1 : c0e2019c  r0 : 00000000
    Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment user
    Control: 30c5387d  Table: 40003000  DAC: 55555555
    Process swapper/0 (pid: 1, stack limit = 0x7eba272f)
    Stack: (0xeb447c00 to 0xeb448000)

    [...]

    [<c03604cc>] (sysfs_create_file_ns) from [<c036051c>] (sysfs_create_files+0x34/0x70)
    [<c036051c>] (sysfs_create_files) from [<c0556288>] (mtd_add_partition_attrs+0x10/0x34)
    [<c0556288>] (mtd_add_partition_attrs) from [<c0556a78>] (add_mtd_partitions+0xd8/0x16c)
    [<c0556a78>] (add_mtd_partitions) from [<c0553f88>] (mtd_device_parse_register+0xc4/0x1b4)
    [<c0553f88>] (mtd_device_parse_register) from [<c055a97c>] (m25p_probe+0x148/0x188)
    [<c055a97c>] (m25p_probe) from [<c055e278>] (spi_drv_probe+0x84/0xa0)

Fix this by ignoring and freeing partitions that failed to add in
add_mtd_partitions().  The same issue is present in mtd_add_partition(),
so fix that as well.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
I don't know if it is worthwhile factoring out the common handling.

Should allocate_partition() fail instead?  There's a comment saying
"let's register it anyway to preserve ordering".
---
 drivers/mtd/mtdpart.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/mtd/mtdpart.c b/drivers/mtd/mtdpart.c
index 023516a632766c42..d41adc1397dcf95e 100644
--- a/drivers/mtd/mtdpart.c
+++ b/drivers/mtd/mtdpart.c
@@ -637,7 +637,14 @@ int mtd_add_partition(struct mtd_info *parent, const char *name,
 	list_add(&new->list, &mtd_partitions);
 	mutex_unlock(&mtd_partitions_mutex);
 
-	add_mtd_device(&new->mtd);
+	ret = add_mtd_device(&new->mtd);
+	if (ret) {
+		mutex_lock(&mtd_partitions_mutex);
+		list_del(&new->list);
+		mutex_unlock(&mtd_partitions_mutex);
+		free_partition(new);
+		return ret;
+	}
 
 	mtd_add_partition_attrs(new);
 
@@ -731,7 +738,7 @@ int add_mtd_partitions(struct mtd_info *master,
 {
 	struct mtd_part *slave;
 	uint64_t cur_offset = 0;
-	int i;
+	int i, ret;
 
 	printk(KERN_NOTICE "Creating %d MTD partitions on \"%s\":\n", nbparts, master->name);
 
@@ -746,7 +753,15 @@ int add_mtd_partitions(struct mtd_info *master,
 		list_add(&slave->list, &mtd_partitions);
 		mutex_unlock(&mtd_partitions_mutex);
 
-		add_mtd_device(&slave->mtd);
+		ret = add_mtd_device(&slave->mtd);
+		if (ret) {
+			mutex_lock(&mtd_partitions_mutex);
+			list_del(&slave->list);
+			mutex_unlock(&mtd_partitions_mutex);
+			free_partition(slave);
+			continue;
+		}
+
 		mtd_add_partition_attrs(slave);
 		if (parts[i].types)
 			mtd_parse_part(slave, parts[i].types);
-- 
2.7.4