When swapon the same S_ISBLK blockdev concurrent, the allocated two
swap_info could hold the same block_device, because claim_swapfile()
allow the same holder(here, it is sys_swapon function).
To prevent this situation, This patch adds swap_lock protect to ensure
we can find this situation and return -EBUSY for one swapon call.
As for S_ISREG swapfile, claim_swapfile() already prevent this scenario
by holding inode->i_mutex.
This patch is just for a rare scenario, aim to correct of code.
Signed-off-by: Weijie Yang <[email protected]>
---
mm/swapfile.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 4d24158..413c213 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2459,9 +2459,10 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
goto bad_swap;
}
+ /* prevent concurrent swapon on the same S_ISBLK blockdev */
+ spin_lock(&swap_lock);
p->swap_file = swap_file;
mapping = swap_file->f_mapping;
-
for (i = 0; i < nr_swapfiles; i++) {
struct swap_info_struct *q = swap_info[i];
@@ -2472,6 +2473,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
goto bad_swap;
}
}
+ spin_unlock(&swap_lock);
inode = mapping->host;
/* If S_ISREG(inode->i_mode) will do mutex_lock(&inode->i_mutex); */
--
1.7.10.4
On Mon, 27 Jan 2014 18:03:04 +0800 Weijie Yang <[email protected]> wrote:
> When swapon the same S_ISBLK blockdev concurrent, the allocated two
> swap_info could hold the same block_device, because claim_swapfile()
> allow the same holder(here, it is sys_swapon function).
>
> To prevent this situation, This patch adds swap_lock protect to ensure
> we can find this situation and return -EBUSY for one swapon call.
>
> As for S_ISREG swapfile, claim_swapfile() already prevent this scenario
> by holding inode->i_mutex.
>
> This patch is just for a rare scenario, aim to correct of code.
>
hm, OK. Would it be saner to pass a unique `holder' to
claim_swapfile()? Say, `p'?
Truly, I am fed up with silly swapon/swapoff races. How often does
anyone call these things? Let's slap a huge lock around the whole
thing and be done with it?
On Mon, 3 Feb 2014, Andrew Morton wrote:
> On Mon, 27 Jan 2014 18:03:04 +0800 Weijie Yang <[email protected]> wrote:
>
> > When swapon the same S_ISBLK blockdev concurrent, the allocated two
> > swap_info could hold the same block_device, because claim_swapfile()
> > allow the same holder(here, it is sys_swapon function).
> >
> > To prevent this situation, This patch adds swap_lock protect to ensure
> > we can find this situation and return -EBUSY for one swapon call.
> >
> > As for S_ISREG swapfile, claim_swapfile() already prevent this scenario
> > by holding inode->i_mutex.
> >
> > This patch is just for a rare scenario, aim to correct of code.
> >
>
> hm, OK. Would it be saner to pass a unique `holder' to
> claim_swapfile()? Say, `p'?
>
> Truly, I am fed up with silly swapon/swapoff races. How often does
> anyone call these things? Let's slap a huge lock around the whole
> thing and be done with it?
That answer makes me sad: we can't be bothered to get it right,
even when Weijie goes to the trouble of presenting a series to do so.
But I sure don't deserve a vote until I've actually looked through it.
Hugh
On Tue, Feb 4, 2014 at 12:20 PM, Hugh Dickins <[email protected]> wrote:
> On Mon, 3 Feb 2014, Andrew Morton wrote:
>> On Mon, 27 Jan 2014 18:03:04 +0800 Weijie Yang <[email protected]> wrote:
>>
>> > When swapon the same S_ISBLK blockdev concurrent, the allocated two
>> > swap_info could hold the same block_device, because claim_swapfile()
>> > allow the same holder(here, it is sys_swapon function).
>> >
>> > To prevent this situation, This patch adds swap_lock protect to ensure
>> > we can find this situation and return -EBUSY for one swapon call.
>> >
>> > As for S_ISREG swapfile, claim_swapfile() already prevent this scenario
>> > by holding inode->i_mutex.
>> >
>> > This patch is just for a rare scenario, aim to correct of code.
>> >
>>
>> hm, OK. Would it be saner to pass a unique `holder' to
>> claim_swapfile()? Say, `p'?
>>
>> Truly, I am fed up with silly swapon/swapoff races. How often does
>> anyone call these things? Let's slap a huge lock around the whole
>> thing and be done with it?
>
> That answer makes me sad: we can't be bothered to get it right,
> even when Weijie goes to the trouble of presenting a series to do so.
> But I sure don't deserve a vote until I've actually looked through it.
>
Hi,
This is a ping email. Could I get some options about these patch series?
Thanks.
> Hugh
On Fri, 18 Apr 2014, Weijie Yang wrote:
> On Tue, Feb 4, 2014 at 12:20 PM, Hugh Dickins <[email protected]> wrote:
> >>
> >> Truly, I am fed up with silly swapon/swapoff races. How often does
> >> anyone call these things? Let's slap a huge lock around the whole
> >> thing and be done with it?
> >
> > That answer makes me sad: we can't be bothered to get it right,
> > even when Weijie goes to the trouble of presenting a series to do so.
> > But I sure don't deserve a vote until I've actually looked through it.
>
> Hi,
>
> This is a ping email. Could I get some options about these patch series?
Sorry, this is no more than a pong in return: I've not lost or
forgotten these, I shall get to them, but priorities intervene.
Hugh