The SCSI core holds scan_mutex around SCSI device addition and
removal operations. sysfs serializes attribute read and write
operations against attribute removal through s_active. Avoid that
grabbing scan_mutex during self-removal of a SCSI device triggers
a deadlock by not calling __kernfs_remove() from
kernfs_remove_by_name_ns() in case of self-removal. This patch
avoids that self-removal triggers the following deadlock:
=======================================================
[ INFO: possible circular locking dependency detected ]
4.9.0-rc1-dbg+ #4 Not tainted
-------------------------------------------------------
test_02_sdev_de/12586 is trying to acquire lock:
(&shost->scan_mutex){+.+.+.}, at: [<ffffffff8148cc5e>]
scsi_remove_device+0x1e/0x40
but task is already holding lock:
(s_active#336){++++.+}, at: [<ffffffff812633fe>] kernfs_remove_self+0xde/0x140
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (s_active#336){++++.+}:
[<ffffffff810bd8b9>] lock_acquire+0xe9/0x1d0
[<ffffffff8126275a>] __kernfs_remove+0x24a/0x310
[<ffffffff812634a0>] kernfs_remove_by_name_ns+0x40/0x90
[<ffffffff81265cc0>] remove_files.isra.1+0x30/0x70
[<ffffffff8126605f>] sysfs_remove_group+0x3f/0x90
[<ffffffff81266159>] sysfs_remove_groups+0x29/0x40
[<ffffffff81450689>] device_remove_attrs+0x59/0x80
[<ffffffff81450f75>] device_del+0x125/0x240
[<ffffffff8148cc03>] __scsi_remove_device+0x143/0x180
[<ffffffff8148ae24>] scsi_forget_host+0x64/0x70
[<ffffffff8147e3f5>] scsi_remove_host+0x75/0x120
[<ffffffffa035dbbb>] 0xffffffffa035dbbb
[<ffffffff81082a65>] process_one_work+0x1f5/0x690
[<ffffffff81082f49>] worker_thread+0x49/0x490
[<ffffffff810897eb>] kthread+0xeb/0x110
[<ffffffff8163ef07>] ret_from_fork+0x27/0x40
-> #0 (&shost->scan_mutex){+.+.+.}:
[<ffffffff810bd31c>] __lock_acquire+0x10fc/0x1270
[<ffffffff810bd8b9>] lock_acquire+0xe9/0x1d0
[<ffffffff8163a49f>] mutex_lock_nested+0x5f/0x360
[<ffffffff8148cc5e>] scsi_remove_device+0x1e/0x40
[<ffffffff8148cca2>] sdev_store_delete+0x22/0x30
[<ffffffff814503a3>] dev_attr_store+0x13/0x20
[<ffffffff81264d60>] sysfs_kf_write+0x40/0x50
[<ffffffff812640c7>] kernfs_fop_write+0x137/0x1c0
[<ffffffff811dd9b3>] __vfs_write+0x23/0x140
[<ffffffff811de080>] vfs_write+0xb0/0x190
[<ffffffff811df374>] SyS_write+0x44/0xa0
[<ffffffff8163ecaa>] entry_SYSCALL_64_fastpath+0x18/0xad
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(s_active#336);
lock(&shost->scan_mutex);
lock(s_active#336);
lock(&shost->scan_mutex);
*** DEADLOCK ***
3 locks held by test_02_sdev_de/12586:
#0: (sb_writers#4){.+.+.+}, at: [<ffffffff811de148>] vfs_write+0x178/0x190
#1: (&of->mutex){+.+.+.}, at: [<ffffffff81264091>]
kernfs_fop_write+0x101/0x1c0
#2: (s_active#336){++++.+}, at: [<ffffffff812633fe>]
kernfs_remove_self+0xde/0x140
stack backtrace:
CPU: 4 PID: 12586 Comm: test_02_sdev_de Not tainted 4.9.0-rc1-dbg+ #4
Call Trace:
[<ffffffff813296c5>] dump_stack+0x68/0x93
[<ffffffff810baafe>] print_circular_bug+0x1be/0x210
[<ffffffff810bd31c>] __lock_acquire+0x10fc/0x1270
[<ffffffff810bd8b9>] lock_acquire+0xe9/0x1d0
[<ffffffff8163a49f>] mutex_lock_nested+0x5f/0x360
[<ffffffff8148cc5e>] scsi_remove_device+0x1e/0x40
[<ffffffff8148cca2>] sdev_store_delete+0x22/0x30
[<ffffffff814503a3>] dev_attr_store+0x13/0x20
[<ffffffff81264d60>] sysfs_kf_write+0x40/0x50
[<ffffffff812640c7>] kernfs_fop_write+0x137/0x1c0
[<ffffffff811dd9b3>] __vfs_write+0x23/0x140
[<ffffffff811de080>] vfs_write+0xb0/0x190
[<ffffffff811df374>] SyS_write+0x44/0xa0
[<ffffffff8163ecaa>] entry_SYSCALL_64_fastpath+0x18/0xad
References: http://www.spinics.net/lists/linux-scsi/msg86551.html
Signed-off-by: Bart Van Assche <bart.vanass...@sandisk.com>
Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Cc: Eric Biederman <ebied...@xmission.com>
Cc: Hannes Reinecke <h...@suse.de>
Cc: Johannes Thumshirn <jthumsh...@suse.de>
Cc: Sagi Grimberg <s...@grimberg.me>
Cc: <sta...@vger.kernel.org>
---
fs/kernfs/dir.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index cf4c636..44ec536 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -1410,7 +1410,7 @@ int kernfs_remove_by_name_ns(struct kernfs_node *parent,
const char *name,
mutex_lock(&kernfs_mutex);
kn = kernfs_find_ns(parent, name, ns);
- if (kn)
+ if (kn && !(kn->flags & KERNFS_SUICIDED))
__kernfs_remove(kn);
mutex_unlock(&kernfs_mutex);
--
2.10.1
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