On Fri, 11 Oct 2013, Andrew Morton wrote: > (cc Hugh) Thank you: I'm sorry, but I have difficulty finding a moment to look.
> > On Fri, 11 Oct 2013 11:54:22 +0200 Krzysztof Kozlowski > <[email protected]> wrote: > > > Swapoff used old_block_size from swap_info which could be overwritten by > > concurrent swapon. > > > > Reported-by: Weijie Yang <[email protected]> > > Signed-off-by: Krzysztof Kozlowski <[email protected]> > > --- > > mm/swapfile.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/mm/swapfile.c b/mm/swapfile.c > > index 3963fc2..de7c904 100644 > > --- a/mm/swapfile.c > > +++ b/mm/swapfile.c > > @@ -1824,6 +1824,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, > > specialfile) > > struct filename *pathname; > > int i, type, prev; > > int err; > > + unsigned int old_block_size; > > > > if (!capable(CAP_SYS_ADMIN)) > > return -EPERM; > > @@ -1914,6 +1915,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, > > specialfile) > > } > > > > swap_file = p->swap_file; > > + old_block_size = p->old_block_size; > > p->swap_file = NULL; > > p->max = 0; > > swap_map = p->swap_map; > > @@ -1938,7 +1940,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, > > specialfile) > > inode = mapping->host; > > if (S_ISBLK(inode->i_mode)) { > > struct block_device *bdev = I_BDEV(inode); > > - set_blocksize(bdev, p->old_block_size); > > + set_blocksize(bdev, old_block_size); > > blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL); > > } else { > > mutex_lock(&inode->i_mutex); > > I find it worrying that a swapon can run concurrently with any of this > swapoff code. It just seem to be asking for trouble and the code > really isn't set up for this and races here will be poorly tested for > > I'm wondering if we should just extend swapon_mutex a lot and eliminate > the concurrency? I have to disagree with you on this. We do not hold swapon_mutex from start to finish of usage of a swap_info_struct, and there's no call to rearrange swapon_mutex usage for this case. It's just a straightforward use of p->old_block_size shortly after *p was freed, and Krzysztof's original patch was the appropriate one. As for more verbiage, well, I'm not so sure that more is better in this case: whichever you find easier to understand. Hugh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
