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Wong" , linux-nvme@lists.infradead.org, Joseph Qi , dm-devel@redhat.com, target-devel@vger.kernel.org, linux-mtd@lists.infradead.org, Jack Wang , Alasdair Kergon , drbd-dev@lists.linbit.com, linux-s390@vger.kernel.org, linux-nilfs@vger.kernel.org, linux-scsi@vger.kernel.org, Sergey Senozhatsky , Christoph Hellwig , xen-devel@lists.xenproject.org, Gao Xiang , Christian Borntraeger , Kent Overstreet , Sven Schnelle , linux-pm@vger.kernel.org, Mike Snitzer , Chao Yu , Joern Engel , reiserfs-devel@vger.kernel.org, linux-block@vger.kernel.org, linux-bcache@vger.kernel.org, Christian Brauner , David Sterba , Jaegeuk Kim , Trond Myklebust , Jens Axboe , linux-raid@vger.kernel.org, linux-nfs@vger.kernel.org, linux-ext4@vger.kernel.org, Ted Tso , linux-mm@kvack.org, Song Liu , linux-f2fs-devel@lists.sourceforge.net, linux-xfs@vger.kernel.org, Minchan Kim , ocfs2-devel@oss.oracle.com, Anna Schumaker , linux-fsdevel@vger.kernel.org, "Md. Haris Iqbal" , Andrew Morton , linux-erofs@lists.ozlabs.org, linux-btrfs@vger.kernel.org Errors-To: dm-devel-bounces@redhat.com Sender: "dm-devel" X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: zeniv.linux.org.uk Content-Disposition: inline Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Fri, Aug 25, 2023 at 03:47:56PM +0200, Jan Kara wrote: > I can see the appeal of not having to introduce the new bdev_handle type > and just using struct file which unifies in-kernel and userspace block > device opens. But I can see downsides too - the last fput() happening from > task work makes me a bit nervous whether it will not break something > somewhere with exclusive bdev opens. Getting from struct file to bdev is > somewhat harder but I guess a helper like F_BDEV() would solve that just > fine. > > So besides my last fput() worry about I think this could work and would be > probably a bit nicer than what I have. But before going and redoing the whole > series let me gather some more feedback so that we don't go back and forth. > Christoph, Christian, Jens, any opinion? Redoing is not an issue - it can be done on top of your series just as well. Async behaviour of fput() might be, but... need to look through the actual users; for a lot of them it's perfectly fine. FWIW, from a cursory look there appears to be a missing primitive: take an opened bdev (or bdev_handle, with your variant, or opened file if we go that way eventually) and claim it. I mean, look at claim_swapfile() for example: p->bdev = blkdev_get_by_dev(inode->i_rdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL, p); if (IS_ERR(p->bdev)) { error = PTR_ERR(p->bdev); p->bdev = NULL; return error; } p->old_block_size = block_size(p->bdev); error = set_blocksize(p->bdev, PAGE_SIZE); if (error < 0) return error; we already have the file opened, and we keep it opened all the way until the swapoff(2); here we have noticed that it's a block device and we * open the fucker again (by device number), this time claiming it with our swap_info_struct as holder, to be closed at swapoff(2) time (just before we close the file) * flip the block size to PAGE_SIZE, to be reverted at swapoff(2) time That really looks like it ought to be * take the opened file, see that it's a block device * try to claim it with that holder * on success, flip the block size with close_filp() in the swapoff(2) (or failure exit path in swapon(2)) doing what it would've done for an O_EXCL opened block device. The only difference from O_EXCL userland open is that here we would end up with holder pointing not to struct file in question, but to our swap_info_struct. It will do the right thing. This extra open is entirely due to "well, we need to claim it and the primitive that does that happens to be tied to opening"; feels rather counter-intuitive. For that matter, we could add an explicit "unclaim" primitive - might be easier to follow. That would add another example where that could be used - in blkdev_bszset() we have an opened block device (it's an ioctl, after all), we want to change block size and we *really* don't want to have that happen under a mounted filesystem. So if it's not opened exclusive, we do a temporary exclusive open of own and act on that instead. Might as well go for a temporary claim... BTW, what happens if two threads call ioctl(fd, BLKBSZSET, &n) for the same descriptor that happens to have been opened O_EXCL? Without O_EXCL they would've been unable to claim the sucker at the same time - the holder we are using is the address of a function argument, i.e. something that points to kernel stack of the caller. Those would conflict and we either get set_blocksize() calls fully serialized, or one of the callers would eat -EBUSY. Not so in "opened with O_EXCL" case - they can very well overlap and IIRC set_blocksize() does *not* expect that kind of crap... It's all under CAP_SYS_ADMIN, so it's not as if it was a meaningful security hole anyway, but it does look fishy. -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel