From: Matthew Wilcox <willy@infradead.org>
To: Jia-Ju Bai <baijiaju1990@gmail.com>
Cc: paul@paul-moore.com, eparis@redhat.com, jack@suse.cz,
amir73il@gmail.com, linux-audit@redhat.com,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] kernel: audit_tree: Fix a sleep-in-atomic-context bug
Date: Wed, 20 Jun 2018 21:29:12 -0700 [thread overview]
Message-ID: <20180621042912.GA4967@bombadil.infradead.org> (raw)
In-Reply-To: <20180621033245.10754-1-baijiaju1990@gmail.com>
On Thu, Jun 21, 2018 at 11:32:45AM +0800, Jia-Ju Bai wrote:
> The kernel may sleep with holding a spinlock.
> The function call paths (from bottom to top) in Linux-4.16.7 are:
>
> [FUNC] kmem_cache_alloc(GFP_KERNEL)
> fs/notify/mark.c, 439:
> kmem_cache_alloc in fsnotify_attach_connector_to_object
> fs/notify/mark.c, 520:
> fsnotify_attach_connector_to_object in fsnotify_add_mark_list
> fs/notify/mark.c, 590:
> fsnotify_add_mark_list in fsnotify_add_mark_locked
> kernel/audit_tree.c, 437:
> fsnotify_add_mark_locked in tag_chunk
> kernel/audit_tree.c, 423:
> spin_lock in tag_chunk
There are several locks here; your report would be improved by saying
which one is the problem. I'm assuming it's old_entry->lock.
spin_lock(&old_entry->lock);
...
if (fsnotify_add_inode_mark_locked(chunk_entry,
old_entry->connector->inode, 1)) {
...
return fsnotify_add_mark_locked(mark, inode, NULL, allow_dups);
...
ret = fsnotify_add_mark_list(mark, inode, mnt, allow_dups);
...
if (inode)
connp = &inode->i_fsnotify_marks;
conn = fsnotify_grab_connector(connp);
if (!conn) {
err = fsnotify_attach_connector_to_object(connp, inode, mnt);
It seems to me that this is safe because old_entry is looked up from
fsnotify_find_mark, and it can't be removed while its lock is held.
Therefore there's always a 'conn' returned from fsnotify_grab_connector(),
and so this path will never be taken.
But this code path is confusing to me, and I could be wrong. Jan, please
confirm my analysis is correct?
> [FUNC] kmem_cache_alloc(GFP_KERNEL)
> fs/notify/mark.c, 439:
> kmem_cache_alloc in fsnotify_attach_connector_to_object
> fs/notify/mark.c, 520:
> fsnotify_attach_connector_to_object in fsnotify_add_mark_list
> fs/notify/mark.c, 590:
> fsnotify_add_mark_list in fsnotify_add_mark_locked
> kernel/audit_tree.c, 291:
> fsnotify_add_mark_locked in untag_chunk
> kernel/audit_tree.c, 258:
> spin_lock in untag_chunk
I'm just going to assume this one is the same.
next prev parent reply other threads:[~2018-06-21 4:29 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-21 3:32 [PATCH] kernel: audit_tree: Fix a sleep-in-atomic-context bug Jia-Ju Bai
2018-06-21 4:29 ` Matthew Wilcox [this message]
2018-06-22 9:23 ` Jan Kara
2018-06-22 18:56 ` Paul Moore
2018-06-25 9:22 ` Jan Kara
2018-06-25 12:55 ` Jan Kara
2018-06-25 22:25 ` Paul Moore
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