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Subject[PATCH v4 38/47] soc: fsl: qe: refactor cpm_muram_alloc_common to prevent BUG on error path
Date
If the kmalloc() fails, we try to undo the gen_pool allocation we've
just done. Unfortunately, start has already been modified to subtract
the GENPOOL_OFFSET bias, so we're freeing something that very likely
doesn't exist in the gen_pool, meaning we hit the

kernel BUG at lib/genalloc.c:399!
Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
...
[<803fd0e8>] (gen_pool_free) from [<80426bc8>] (cpm_muram_alloc_common+0xb0/0xc8)
[<80426bc8>] (cpm_muram_alloc_common) from [<80426c28>] (cpm_muram_alloc+0x48/0x80)
[<80426c28>] (cpm_muram_alloc) from [<80428214>] (ucc_slow_init+0x110/0x4f0)
[<80428214>] (ucc_slow_init) from [<8044a718>] (qe_uart_request_port+0x3c/0x1d8)

(this was tested by just injecting a random failure by adding
"|| (get_random_int()&7) == 0" to the "if (!entry)" condition).

Refactor the code so we do the kmalloc() first, meaning that's the
thing that needs undoing in case gen_pool_alloc_algo() then
fails. This allows a later cleanup to move the locking from the
callers into the _common function, keeping the kmalloc() out of the
critical region and then, hopefully (if all the muram_alloc callers
allow) change it to a GFP_KERNEL allocation.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
drivers/soc/fsl/qe/qe_common.c | 16 +++++++---------
1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/drivers/soc/fsl/qe/qe_common.c b/drivers/soc/fsl/qe/qe_common.c
index feb33ec1c3d6..bc9b436684df 100644
--- a/drivers/soc/fsl/qe/qe_common.c
+++ b/drivers/soc/fsl/qe/qe_common.c
@@ -119,23 +119,21 @@ static s32 cpm_muram_alloc_common(unsigned long size,
struct muram_block *entry;
s32 start;

+ entry = kmalloc(sizeof(*entry), GFP_ATOMIC);
+ if (!entry)
+ return -ENOMEM;
start = gen_pool_alloc_algo(muram_pool, size, algo, data);
- if (!start)
- goto out2;
+ if (!start) {
+ kfree(entry);
+ return -ENOMEM;
+ }
start = start - GENPOOL_OFFSET;
memset_io(cpm_muram_addr(start), 0, size);
- entry = kmalloc(sizeof(*entry), GFP_ATOMIC);
- if (!entry)
- goto out1;
entry->start = start;
entry->size = size;
list_add(&entry->head, &muram_block_list);

return start;
-out1:
- gen_pool_free(muram_pool, start, size);
-out2:
- return -ENOMEM;
}

/*
--
2.23.0
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