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Wong" To: Naohiro Aota Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, Andrew Morton , Christoph Hellwig Subject: Re: [PATCH] mm, swap: unlock inode in error path of claim_swapfile Message-ID: <20200204235608.GG6874@magnolia> References: <20200204095943.727666-1-naohiro.aota@wdc.com> <20200204154229.GC6874@magnolia> <20200204234916.s6zx6i2ko4mvxim2@naota.dhcp.fujisawa.hgst.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200204234916.s6zx6i2ko4mvxim2@naota.dhcp.fujisawa.hgst.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9521 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=2 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-2001150001 definitions=main-2002040163 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9521 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-2001150001 definitions=main-2002040163 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Feb 05, 2020 at 08:49:16AM +0900, Naohiro Aota wrote: > On Tue, Feb 04, 2020 at 07:42:29AM -0800, Darrick J. Wong wrote: > > On Tue, Feb 04, 2020 at 06:59:43PM +0900, Naohiro Aota wrote: > > > claim_swapfile() currently keeps the inode locked when it is successful, or > > > the file is already swapfile (with -EBUSY). And, on the other error cases, > > > it does not lock the inode. > > > > > > This inconsistency of the lock state and return value is quite confusing > > > and actually causing a bad unlock balance as below in the "bad_swap" > > > section of __do_sys_swapon(). > > > > > > This commit fixes this issue by unlocking the inode on the error path. It > > > also reverts blocksize and releases bdev, so that the caller can safely > > > forget about the inode. > > > > > > ===================================== > > > WARNING: bad unlock balance detected! > > > 5.5.0-rc7+ #176 Not tainted > > > ------------------------------------- > > > swapon/4294 is trying to release lock (&sb->s_type->i_mutex_key) at: > > > [] __do_sys_swapon+0x94b/0x3550 > > > but there are no more locks to release! > > > > > > other info that might help us debug this: > > > no locks held by swapon/4294. > > > > > > stack backtrace: > > > CPU: 5 PID: 4294 Comm: swapon Not tainted 5.5.0-rc7-BTRFS-ZNS+ #176 > > > Hardware name: ASUS All Series/H87-PRO, BIOS 2102 07/29/2014 > > > Call Trace: > > > dump_stack+0xa1/0xea > > > ? __do_sys_swapon+0x94b/0x3550 > > > print_unlock_imbalance_bug.cold+0x114/0x123 > > > ? __do_sys_swapon+0x94b/0x3550 > > > lock_release+0x562/0xed0 > > > ? kvfree+0x31/0x40 > > > ? lock_downgrade+0x770/0x770 > > > ? kvfree+0x31/0x40 > > > ? rcu_read_lock_sched_held+0xa1/0xd0 > > > ? rcu_read_lock_bh_held+0xb0/0xb0 > > > up_write+0x2d/0x490 > > > ? kfree+0x293/0x2f0 > > > __do_sys_swapon+0x94b/0x3550 > > > ? putname+0xb0/0xf0 > > > ? kmem_cache_free+0x2e7/0x370 > > > ? do_sys_open+0x184/0x3e0 > > > ? generic_max_swapfile_size+0x40/0x40 > > > ? do_syscall_64+0x27/0x4b0 > > > ? entry_SYSCALL_64_after_hwframe+0x49/0xbe > > > ? lockdep_hardirqs_on+0x38c/0x590 > > > __x64_sys_swapon+0x54/0x80 > > > do_syscall_64+0xa4/0x4b0 > > > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > > RIP: 0033:0x7f15da0a0dc7 > > > > > > Fixes: 1638045c3677 ("mm: set S_SWAPFILE on blockdev swap devices") > > > Signed-off-by: Naohiro Aota > > > --- > > > mm/swapfile.c | 29 ++++++++++++++++++++++------- > > > 1 file changed, 22 insertions(+), 7 deletions(-) > > > > > > diff --git a/mm/swapfile.c b/mm/swapfile.c > > > index bb3261d45b6a..dd5d7fa42282 100644 > > > --- a/mm/swapfile.c > > > +++ b/mm/swapfile.c > > > @@ -2886,24 +2886,37 @@ static int claim_swapfile(struct swap_info_struct *p, struct inode *inode) > > > p->old_block_size = block_size(p->bdev); > > > error = set_blocksize(p->bdev, PAGE_SIZE); > > > if (error < 0) > > > - return error; > > > + goto err; > > > /* > > > * Zoned block devices contain zones that have a sequential > > > * write only restriction. Hence zoned block devices are not > > > * suitable for swapping. Disallow them here. > > > */ > > > - if (blk_queue_is_zoned(p->bdev->bd_queue)) > > > - return -EINVAL; > > > + if (blk_queue_is_zoned(p->bdev->bd_queue)) { > > > + error = -EINVAL; > > > + goto err; > > > + } > > > p->flags |= SWP_BLKDEV; > > > } else if (S_ISREG(inode->i_mode)) { > > > p->bdev = inode->i_sb->s_bdev; > > > } > > > > > > inode_lock(inode); > > > - if (IS_SWAPFILE(inode)) > > > - return -EBUSY; > > > + if (IS_SWAPFILE(inode)) { > > > + inode_unlock(inode); > > > + error = -EBUSY; > > > + goto err; > > > + } > > > > > > return 0; > > > + > > > +err: > > > + if (S_ISBLK(inode->i_mode)) { > > > + set_blocksize(p->bdev, p->old_block_size); > > > + blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL); > > > + } > > > + > > > + return error; > > > } > > > > > > > > > @@ -3157,10 +3170,12 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) > > > mapping = swap_file->f_mapping; > > > inode = mapping->host; > > > > > > - /* If S_ISREG(inode->i_mode) will do inode_lock(inode); */ > > > + /* do inode_lock(inode); */ > > > > What if we made this function responsible for calling inode_lock (and > > unlock) instead of splitting it between sys_swapon and claim_swapfile? > > I think we cannot take inode_lock before claim_swapfile() because we can > have circular locking dependency as: > > claim_swapfile() > -> blkdev_get() -> __blkdev_get() > -> mutex_lock(&bdev->bd_mutex) > -> bd_set_size() > -> inode_lock(&bdev->bd_inode); Ah, good point. Thank you for doing the research on that. :) > So, one thing we can do is to move inode_lock() and "if (IS_SWAPFILE(..)) > ..." out of claim_swapfile(). In this case, the "bad_swap" section must > check if "inode_is_locked" to call "inode_unlock". I think I wouldn't rely on inode_is_locked and structure the error escape as follows: err = claim_swapfile() if (err) goto bad_swap; inode_lock() if (IS_SWAPFILE) goto unlock_swap; other_stuff() unlock_swap: inode_unlock() bad_swap: fput() since that's how we (well, XFS anyway :)) tend to do it. --D > > > > --D > > > > > error = claim_swapfile(p, inode); > > > - if (unlikely(error)) > > > + if (unlikely(error)) { > > > + inode = NULL; > > > goto bad_swap; > > > + } > > > > > > /* > > > * Read the swap header. > > > -- > > > 2.25.0 > > >