linux-ext4 - Re: [RFC PATCH] coredump: avoid ext4 auto_da

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Message-ID: <e906173a-a589-ec6a-73e0-ecf899e86b0e@fb.com>
Date:	Tue, 5 Jul 2016 11:01:40 -0400
From:	Josef Bacik <jbacik@...com>
To:	"Theodore Ts'o" <tytso@....edu>
CC:	Omar Sandoval <osandov@...ndov.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	<linux-fsdevel@...r.kernel.org>, <linux-ext4@...r.kernel.org>,
	<kernel-team@...com>
Subject: Re: [RFC PATCH] coredump: avoid ext4 auto_da_alloc for core file

On 07/05/2016 10:37 AM, Theodore Ts'o wrote:
> On Tue, Jul 05, 2016 at 09:42:13AM -0400, Josef Bacik wrote:
>>> diff --git a/fs/coredump.c b/fs/coredump.c
>>> index 281b768000e6..9da7357773f0 100644
>>> --- a/fs/coredump.c
>>> +++ b/fs/coredump.c
>>> @@ -741,8 +741,10 @@ void do_coredump(const siginfo_t *siginfo)
>>>  			goto close_fail;
>>>  		if (!(cprm.file->f_mode & FMODE_CAN_WRITE))
>>>  			goto close_fail;
>>> -		if (do_truncate(cprm.file->f_path.dentry, 0, 0, cprm.file))
>>> -			goto close_fail;
>>> +		if (i_size_read(file_inode(cprm.file)) != 0) {
>>> +			if (do_truncate(cprm.file->f_path.dentry, 0, 0, cprm.file))
>>> +				goto close_fail;
>>> +		}
>>>  	}
>>>
>>>  	/* get us an unshared descriptor table; almost always a no-op */
>>>
>>
>> Omar, this probably breaks the case where we do
>> fallocate(FALLOC_FL_KEEP_SIZE), the i_size will be 0 but there will be
>> blocks to truncate.  Probably want to check i_blocks or something.  Thanks,
>
> Sure, but this is in the coredump code; do we care there?  What are
> the odds that someone will have fallocated blocks beyond i_size in a
> file named "core"?  And if so, it's not like it's going to make the
> coredump invalid or non-useful in any way.

Wow I totally didn't notice this was in coredump.c, I thought it was in ext4 
code because you said it failed regression tests, which I assumed were your ext4 
tests.  Ignore me.  Thanks,

Josef

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