From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
This fix the below reported false lockdep warning. e096d0c7e2e4e5893792db865dd065ac73cf1f00
did a similar annotation for every other inode in hugetlbfs but missed the root
inode because it was allocated by a separate function.
For HugeTLB fs we allow taking i_mutex in mmap. HugeTLB fs doesn't support file
write and its file read callback is modified in a05b0855fd15504972dba2358e5faa172a1e50ba
to not take i_mutex. Hence for HugeTLB fs with regular files we really don't take
i_mutex with mmap_sem held.
======================================================
[ INFO: possible circular locking dependency detected ]
3.4.0-rc1+ #322 Not tainted
-------------------------------------------------------
bash/1572 is trying to acquire lock:
(&mm->mmap_sem){++++++}, at: [<ffffffff810f1618>] might_fault+0x40/0x90
but task is already holding lock:
(&sb->s_type->i_mutex_key#12){+.+.+.}, at: [<ffffffff81125f88>] vfs_readdir+0x56/0xa8
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&sb->s_type->i_mutex_key#12){+.+.+.}:
[<ffffffff810a09e5>] lock_acquire+0xd5/0xfa
[<ffffffff816a2f5e>] __mutex_lock_common+0x48/0x350
[<ffffffff816a3325>] mutex_lock_nested+0x2a/0x31
[<ffffffff811fb8e1>] hugetlbfs_file_mmap+0x7d/0x104
[<ffffffff810f859a>] mmap_region+0x272/0x47d
[<ffffffff810f8a39>] do_mmap_pgoff+0x294/0x2ee
[<ffffffff810f8b65>] sys_mmap_pgoff+0xd2/0x10e
[<ffffffff8103d19e>] sys_mmap+0x1d/0x1f
[<ffffffff816a5922>] system_call_fastpath+0x16/0x1b
-> #0 (&mm->mmap_sem){++++++}:
[<ffffffff810a0256>] __lock_acquire+0xa81/0xd75
[<ffffffff810a09e5>] lock_acquire+0xd5/0xfa
[<ffffffff810f1645>] might_fault+0x6d/0x90
[<ffffffff81125d62>] filldir+0x6a/0xc2
[<ffffffff81133a83>] dcache_readdir+0x5c/0x222
[<ffffffff81125fa8>] vfs_readdir+0x76/0xa8
[<ffffffff811260b6>] sys_getdents+0x79/0xc9
[<ffffffff816a5922>] system_call_fastpath+0x16/0x1b
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&sb->s_type->i_mutex_key#12);
lock(&mm->mmap_sem);
lock(&sb->s_type->i_mutex_key#12);
lock(&mm->mmap_sem);
*** DEADLOCK ***
1 lock held by bash/1572:
#0: (&sb->s_type->i_mutex_key#12){+.+.+.}, at: [<ffffffff81125f88>] vfs_readdir+0x56/0xa8
stack backtrace:
Pid: 1572, comm: bash Not tainted 3.4.0-rc1+ #322
Call Trace:
[<ffffffff81699a3c>] print_circular_bug+0x1f8/0x209
[<ffffffff810a0256>] __lock_acquire+0xa81/0xd75
[<ffffffff810f38aa>] ? handle_pte_fault+0x5ff/0x614
[<ffffffff8109e622>] ? mark_lock+0x2d/0x258
[<ffffffff810f1618>] ? might_fault+0x40/0x90
[<ffffffff810a09e5>] lock_acquire+0xd5/0xfa
[<ffffffff810f1618>] ? might_fault+0x40/0x90
[<ffffffff816a3249>] ? __mutex_lock_common+0x333/0x350
[<ffffffff810f1645>] might_fault+0x6d/0x90
[<ffffffff810f1618>] ? might_fault+0x40/0x90
[<ffffffff81125d62>] filldir+0x6a/0xc2
[<ffffffff81133a83>] dcache_readdir+0x5c/0x222
[<ffffffff81125cf8>] ? sys_ioctl+0x74/0x74
[<ffffffff81125cf8>] ? sys_ioctl+0x74/0x74
[<ffffffff81125cf8>] ? sys_ioctl+0x74/0x74
[<ffffffff81125fa8>] vfs_readdir+0x76/0xa8
[<ffffffff811260b6>] sys_getdents+0x79/0xc9
[<ffffffff816a5922>] system_call_fastpath+0x16/0x1b
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
---
fs/hugetlbfs/inode.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 92f75aa..d8899e1 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -485,6 +485,7 @@ static struct inode *hugetlbfs_get_root(struct super_block *sb,
inode->i_fop = &simple_dir_operations;
/* directory inodes start off with i_nlink == 2 (for "." entry) */
inc_nlink(inode);
+ lockdep_annotate_inode_mutex_key(inode);
}
return inode;
}
--
1.7.10
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