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mm/swapfile.c: move inode_lock out of claim_swapfile
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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 moving the inode_lock() and IS_SWAPFILE
check out of claim_swapfile().  The inode is unlocked in
"bad_swap_unlock_inode" section, so that the inode is ensured to be
unlocked at "bad_swap".  Thus, error handling codes after the locking now
jumps to "bad_swap_unlock_inode" instead of "bad_swap".

    =====================================
    WARNING: bad unlock balance detected!
    5.5.0-rc7+ torvalds#176 Not tainted
    -------------------------------------
    swapon/4294 is trying to release lock (&sb->s_type->i_mutex_key) at:
    [<ffffffff8173a6eb>] __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+ torvalds#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

Link: http://lkml.kernel.org/r/20200206090132.154869-1-naohiro.aota@wdc.com
Fixes: 1638045 ("mm: set S_SWAPFILE on blockdev swap devices")
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
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@naota @sfrothwell
naota authored and sfrothwell committed Feb 15, 2020
1 parent 04df87b commit dddfe6d
Showing 1 changed file with 20 additions and 21 deletions.
41 changes: 20 additions & 21 deletions mm/swapfile.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2899,10 +2899,6 @@ static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
p->bdev = inode->i_sb->s_bdev;
}

inode_lock(inode);
if (IS_SWAPFILE(inode))
return -EBUSY;

return 0;
}

Expand Down Expand Up @@ -3157,36 +3153,41 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
mapping = swap_file->f_mapping;
inode = mapping->host;

/* will take i_rwsem; */
error = claim_swapfile(p, inode);
if (unlikely(error))
goto bad_swap;

inode_lock(inode);
if (IS_SWAPFILE(inode)) {
error = -EBUSY;
goto bad_swap_unlock_inode;
}

/*
* Read the swap header.
*/
if (!mapping->a_ops->readpage) {
error = -EINVAL;
goto bad_swap;
goto bad_swap_unlock_inode;
}
page = read_mapping_page(mapping, 0, swap_file);
if (IS_ERR(page)) {
error = PTR_ERR(page);
goto bad_swap;
goto bad_swap_unlock_inode;
}
swap_header = kmap(page);

maxpages = read_swap_header(p, swap_header, inode);
if (unlikely(!maxpages)) {
error = -EINVAL;
goto bad_swap;
goto bad_swap_unlock_inode;
}

/* OK, set up the swap map and apply the bad block list */
swap_map = vzalloc(maxpages);
if (!swap_map) {
error = -ENOMEM;
goto bad_swap;
goto bad_swap_unlock_inode;
}

if (bdi_cap_stable_pages_required(inode_to_bdi(inode)))
Expand All @@ -3211,7 +3212,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
GFP_KERNEL);
if (!cluster_info) {
error = -ENOMEM;
goto bad_swap;
goto bad_swap_unlock_inode;
}

for (ci = 0; ci < nr_cluster; ci++)
Expand All @@ -3220,7 +3221,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
p->percpu_cluster = alloc_percpu(struct percpu_cluster);
if (!p->percpu_cluster) {
error = -ENOMEM;
goto bad_swap;
goto bad_swap_unlock_inode;
}
for_each_possible_cpu(cpu) {
struct percpu_cluster *cluster;
Expand All @@ -3234,13 +3235,13 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)

error = swap_cgroup_swapon(p->type, maxpages);
if (error)
goto bad_swap;
goto bad_swap_unlock_inode;

nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
cluster_info, maxpages, &span);
if (unlikely(nr_extents < 0)) {
error = nr_extents;
goto bad_swap;
goto bad_swap_unlock_inode;
}
/* frontswap enabled? set up bit-per-page map for frontswap */
if (IS_ENABLED(CONFIG_FRONTSWAP))
Expand Down Expand Up @@ -3280,7 +3281,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)

error = init_swap_address_space(p->type, maxpages);
if (error)
goto bad_swap;
goto bad_swap_unlock_inode;

/*
* Flush any pending IO and dirty mappings before we start using this
Expand All @@ -3290,7 +3291,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
error = inode_drain_writes(inode);
if (error) {
inode->i_flags &= ~S_SWAPFILE;
goto bad_swap;
goto bad_swap_unlock_inode;
}

mutex_lock(&swapon_mutex);
Expand All @@ -3315,13 +3316,16 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)

error = 0;
goto out;
bad_swap_unlock_inode:
inode_unlock(inode);
bad_swap:
free_percpu(p->percpu_cluster);
p->percpu_cluster = NULL;
if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
set_blocksize(p->bdev, p->old_block_size);
blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
}
inode = NULL;
destroy_swap_extents(p);
swap_cgroup_swapoff(p->type);
spin_lock(&swap_lock);
Expand All @@ -3333,13 +3337,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
kvfree(frontswap_map);
if (inced_nr_rotate_swap)
atomic_dec(&nr_rotate_swap);
if (swap_file) {
if (inode) {
inode_unlock(inode);
inode = NULL;
}
if (swap_file)
filp_close(swap_file, NULL);
}
out:
if (page && !IS_ERR(page)) {
kunmap(page);
Expand Down

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