This is a second attempt at the fix for the list_del corruption
issue. This patch adds a similar refcount approach in
clean_demultiplex_info() since that was noticed. However, for
some reason I now get the list_del corruption come back fairly
quickly (after a few minutes) and eventually a softlockup.
I have not tracked down the problem yet.
There's a race between the demultiplexer thread and the request
issuing thread similar to the race described in
commit 696e420bb2a6 ("cifs: Fix use after free of a mid_q_entry")
where both threads may obtain and attempt to call list_del_init
on the same mid and a list_del corruption similar to the
following will result:
[ 430.454897] list_del corruption. prev->next should be ffff98d3a8f316c0, but was 2e885cb266355469
[ 430.464668] ------------[ cut here ]------------
[ 430.466569] kernel BUG at lib/list_debug.c:51!
[ 430.468476] invalid opcode: 0000 [#1] SMP PTI
[ 430.470286] CPU: 0 PID: 13267 Comm: cifsd Kdump: loaded Not tainted 5.4.0-rc3+ #19
[ 430.473472] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
[ 430.475872] RIP: 0010:__list_del_entry_valid.cold+0x31/0x55
[ 430.478129] Code: 5e 15 8e e8 54 a3 c5 ff 0f 0b 48 c7 c7 78 5f 15 8e e8 46 a3 c5 ff 0f 0b 48 89 f2 48 89 fe 48 c7 c7 38 5f 15 8e e8 32 a3 c5 ff <0f> 0b 48 89 fe 4c 89 c2 48 c7 c7 00 5f 15 8e e8 1e a3 c5 ff 0f 0b
[ 430.485563] RSP: 0018:ffffb4db0042fd38 EFLAGS: 00010246
[ 430.487665] RAX: 0000000000000054 RBX: ffff98d3aabb8800 RCX: 0000000000000000
[ 430.490513] RDX: 0000000000000000 RSI: ffff98d3b7a17908 RDI: ffff98d3b7a17908
[ 430.493383] RBP: ffff98d3a8f316c0 R08: ffff98d3b7a17908 R09: 0000000000000285
[ 430.496258] R10: ffffb4db0042fbf0 R11: ffffb4db0042fbf5 R12: ffff98d3aabb89c0
[ 430.499113] R13: ffffb4db0042fd48 R14: 2e885cb266355469 R15: ffff98d3b24c4480
[ 430.501981] FS: 0000000000000000(0000) GS:ffff98d3b7a00000(0000) knlGS:0000000000000000
[ 430.505232] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 430.507546] CR2: 00007f08cd17b9c0 CR3: 000000023484a000 CR4: 00000000000406f0
[ 430.510426] Call Trace:
[ 430.511500] cifs_reconnect+0x25e/0x610 [cifs]
[ 430.513350] cifs_readv_from_socket+0x220/0x250 [cifs]
[ 430.515464] cifs_read_from_socket+0x4a/0x70 [cifs]
[ 430.517452] ? try_to_wake_up+0x212/0x650
[ 430.519122] ? cifs_small_buf_get+0x16/0x30 [cifs]
[ 430.521086] ? allocate_buffers+0x66/0x120 [cifs]
[ 430.523019] cifs_demultiplex_thread+0xdc/0xc30 [cifs]
[ 430.525116] kthread+0xfb/0x130
[ 430.526421] ? cifs_handle_standard+0x190/0x190 [cifs]
[ 430.528514] ? kthread_park+0x90/0x90
[ 430.530019] ret_from_fork+0x35/0x40
To fix the above, inside cifs_reconnect unconditionally set the
state to MID_RETRY_NEEDED, and then take a reference before we
move any mid_q_entry on server->pending_mid_q to the temporary
retry_list. Then while processing retry_list make sure we check
the state is still MID_RETRY_NEEDED while holding GlobalMid_Lock
before calling list_del_init. Then after mid_q_entry callback
has been completed, drop the reference. In the code paths for
request issuing thread, avoid calling list_del_init if we
notice mid->mid_state != MID_RETRY_NEEDED, avoiding the
race and duplicate call to list_del_init. In addition to
the above MID_RETRY_NEEDED case, handle the MID_SHUTDOWN case
in a similar fashion to avoid the possibility of a similar
crash.
Signed-off-by: Dave Wysochanski <dwysocha@xxxxxxxxxx>
Reviewed-by: Ronnie Sahlberg <lsahlber@xxxxxxxxxx>
---
fs/cifs/connect.c | 30 ++++++++++++++++++++++--------
fs/cifs/transport.c | 8 ++++++--
2 files changed, 28 insertions(+), 10 deletions(-)
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index a64dfa95a925..0327bace214d 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -564,8 +564,9 @@ cifs_reconnect(struct TCP_Server_Info *server)
spin_lock(&GlobalMid_Lock);
list_for_each_safe(tmp, tmp2, &server->pending_mid_q) {
mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
- if (mid_entry->mid_state == MID_REQUEST_SUBMITTED)
- mid_entry->mid_state = MID_RETRY_NEEDED;
+ kref_get(&mid_entry->refcount);
+ WARN_ON(mid_entry->mid_state != MID_REQUEST_SUBMITTED);
+ mid_entry->mid_state = MID_RETRY_NEEDED;
list_move(&mid_entry->qhead, &retry_list);
}
spin_unlock(&GlobalMid_Lock);
@@ -574,8 +575,12 @@ cifs_reconnect(struct TCP_Server_Info *server)
cifs_dbg(FYI, "%s: issuing mid callbacks\n", __func__);
list_for_each_safe(tmp, tmp2, &retry_list) {
mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
- list_del_init(&mid_entry->qhead);
+ spin_lock(&GlobalMid_Lock);
+ if (mid_entry->mid_state == MID_RETRY_NEEDED)
+ list_del_init(&mid_entry->qhead);
+ spin_unlock(&GlobalMid_Lock);
mid_entry->callback(mid_entry);
+ cifs_mid_q_entry_release(mid_entry);
}
if (cifs_rdma_enabled(server)) {
@@ -884,10 +889,6 @@ dequeue_mid(struct mid_q_entry *mid, bool malformed)
mid->when_received = jiffies;
#endif
spin_lock(&GlobalMid_Lock);
- if (!malformed)
- mid->mid_state = MID_RESPONSE_RECEIVED;
- else
- mid->mid_state = MID_RESPONSE_MALFORMED;
/*
* Trying to handle/dequeue a mid after the send_recv()
* function has finished processing it is a bug.
@@ -895,8 +896,15 @@ dequeue_mid(struct mid_q_entry *mid, bool malformed)
if (mid->mid_flags & MID_DELETED)
printk_once(KERN_WARNING
"trying to dequeue a deleted mid\n");
- else
+ if (mid->mid_state != MID_RETRY_NEEDED &&
+ mid->mid_state != MID_SHUTDOWN)
list_del_init(&mid->qhead);
+
+ if (!malformed)
+ mid->mid_state = MID_RESPONSE_RECEIVED;
+ else
+ mid->mid_state = MID_RESPONSE_MALFORMED;
+
spin_unlock(&GlobalMid_Lock);
}
@@ -966,6 +974,7 @@ static void clean_demultiplex_info(struct TCP_Server_Info *server)
list_for_each_safe(tmp, tmp2, &server->pending_mid_q) {
mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
cifs_dbg(FYI, "Clearing mid 0x%llx\n", mid_entry->mid);
+ kref_get(&mid_entry->refcount);
mid_entry->mid_state = MID_SHUTDOWN;
list_move(&mid_entry->qhead, &dispose_list);
}
@@ -975,8 +984,13 @@ static void clean_demultiplex_info(struct TCP_Server_Info *server)
list_for_each_safe(tmp, tmp2, &dispose_list) {
mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
cifs_dbg(FYI, "Callback mid 0x%llx\n", mid_entry->mid);
+ spin_lock(&GlobalMid_Lock);
+ if (mid_entry->mid_state == MID_SHUTDOWN)
+ list_del_init(&mid_entry->qhead);
+ spin_unlock(&GlobalMid_Lock);
list_del_init(&mid_entry->qhead);
mid_entry->callback(mid_entry);
+ cifs_mid_q_entry_release(mid_entry);
}
/* 1/8th of sec is more than enough time for them to exit */
msleep(125);
diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
index 308ad0f495e1..d1794bd664ae 100644
--- a/fs/cifs/transport.c
+++ b/fs/cifs/transport.c
@@ -173,7 +173,9 @@ void
cifs_delete_mid(struct mid_q_entry *mid)
{
spin_lock(&GlobalMid_Lock);
- list_del_init(&mid->qhead);
+ if (mid->mid_state != MID_RETRY_NEEDED &&
+ mid->mid_state != MID_SHUTDOWN)
+ list_del_init(&mid->qhead);
mid->mid_flags |= MID_DELETED;
spin_unlock(&GlobalMid_Lock);
@@ -872,7 +874,9 @@ cifs_sync_mid_result(struct mid_q_entry *mid, struct TCP_Server_Info *server)
rc = -EHOSTDOWN;
break;
default:
- list_del_init(&mid->qhead);
+ if (mid->mid_state != MID_RETRY_NEEDED &&
+ mid->mid_state != MID_SHUTDOWN)
+ list_del_init(&mid->qhead);
cifs_server_dbg(VFS, "%s: invalid mid state mid=%llu state=%d\n",
__func__, mid->mid, mid->mid_state);
rc = -EIO;
--
2.21.0
