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 <weijie.yang@xxxxxxxxxxx>
---
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
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