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SubjectRe: [PATCH] fs: nfs: fix a possible sleep-in-atomic-context bug in _pnfs_grab_empty_layout()
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On 2019/12/17 22:37, Trond Myklebust wrote:
> On Tue, 2019-12-17 at 21:33 +0800, Jia-Ju Bai wrote:
>> The filesystem may sleep while holding a spinlock.
>> The function call path (from bottom to top) in Linux 4.19 is:
>>
>> fs/nfs/pnfs.c, 2052:
>> pnfs_find_alloc_layout(GFP_KERNEL) in _pnfs_grab_empty_layout
>> fs/nfs/pnfs.c, 2051:
>> spin_lock in _pnfs_grab_empty_layout
>>
>> pnfs_find_alloc_layout(GFP_KERNEL) can sleep at runtime.
>>
>> To fix this possible bug, GFP_KERNEL is replaced with GFP_ATOMIC for
>> pnfs_find_alloc_layout().
>>
>> This bug is found by a static analysis tool STCheck written by
>> myself.
>>
>> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
>> ---
>> fs/nfs/pnfs.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
>> index cec3070ab577..cfbe170f0651 100644
>> --- a/fs/nfs/pnfs.c
>> +++ b/fs/nfs/pnfs.c
>> @@ -2138,7 +2138,7 @@ _pnfs_grab_empty_layout(struct inode *ino,
>> struct nfs_open_context *ctx)
>> struct pnfs_layout_hdr *lo;
>>
>> spin_lock(&ino->i_lock);
>> - lo = pnfs_find_alloc_layout(ino, ctx, GFP_KERNEL);
>> + lo = pnfs_find_alloc_layout(ino, ctx, GFP_ATOMIC);
>> if (!lo)
>> goto out_unlock;
>> if (!test_bit(NFS_LAYOUT_INVALID_STID, &lo->plh_flags))
> I'm not seeing why this is necessary. As far as I can see,
> pnfs_find_alloc_layout() will release the ino->i_lock before sleeping.
>
> False positive?
>

Thanks for the reply.
You are right, my report is false...
I did not check the definition of pnfs_find_alloc_layout(), sorry...


Best wishes,
Jia-Ju Bai

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