[PATCH rdma-rc] RDMA/core: Fix race between alloc_uobj and destroy_fd

[Leon Romanovsky <leon@kernel.org>]

From: Leon Romanovsky <leonro@mellanox.com>

Both new object allocation and FD destroy paths hold UVERBS_LOOKUP_WRITE,
the race between them causes the following dump stack.

[  268.688470] ------------[ cut here ]------------
[  268.689460] WARNING: CPU: 4 PID: 6913 at drivers/infiniband/core/rdma_core.c:768 uverbs_uobject_fd_release+0x202/0x230
[  268.691322] Kernel panic - not syncing: panic_on_warn set ...
[  268.692273] CPU: 4 PID: 6913 Comm: syz-executor.3 Not tainted 5.7.0-rc2 #22
[  268.693456] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 04/01/2014
[  268.695688] Call Trace:
[  268.696135]  dump_stack+0x94/0xce
[  268.696784]  panic+0x234/0x56f
[  268.697384]  ? __warn+0x1e1/0x1e1
[  268.697942]  ? kmsg_dump_rewind_nolock+0xd9/0xd9
[  268.698782]  ? printk+0xb2/0xdd
[  268.699301]  ? __warn+0x1b1/0x1e1
[  268.699946]  ? uverbs_uobject_fd_release+0x202/0x230
[  268.700829]  __warn+0x1cc/0x1e1
[  268.701402]  ? uverbs_uobject_fd_release+0x202/0x230
[  268.702227]  report_bug+0x200/0x310
[  268.702807]  ? uverbs_uobject_fd_release+0x202/0x230
[  268.703618]  fixup_bug.part.11+0x32/0x80
[  268.704260]  do_error_trap+0xd3/0x100
[  268.704898]  do_invalid_op+0x31/0x40
[  268.705581]  ? uverbs_uobject_fd_release+0x202/0x230
[  268.706479]  invalid_op+0x1e/0x30
[  268.707035] RIP: 0010:uverbs_uobject_fd_release+0x202/0x230
[  268.708046] Code: fe 4c 89 e7 e8 af 23 fe ff e9 2a ff ff ff e8 c5 fa 61 fe be 03 00 00 00 4c 89 e7 e8 68 eb f5 fe e9 13 ff ff ff e8 ae fa 61 fe <0f> 0b eb ac e8 e5 aa 3c fe e8 50 2b 86 fe e9 6a fe ff ff e8 46 2b
[  268.711365] RSP: 0018:ffffc90008117d88 EFLAGS: 00010293
[  268.712218] RAX: ffff88810e146580 RBX: 1ffff92001022fb1 RCX: ffffffff82d5b902
[  268.713439] RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffff88811951b040
[  268.714606] RBP: ffff88811951b000 R08: ffffed10232a3609 R09: ffffed10232a3609
[  268.715805] R10: ffff88811951b043 R11: 0000000000000001 R12: ffff888100a7c600
[  268.717119] R13: ffff888100a7c650 R14: ffffc90008117da8 R15: ffffffff82d5b700
[  268.718401]  ? __uverbs_cleanup_ufile+0x270/0x270
[  268.719181]  ? uverbs_uobject_fd_release+0x202/0x230
[  268.720140]  ? uverbs_uobject_fd_release+0x202/0x230
[  268.720967]  ? __uverbs_cleanup_ufile+0x270/0x270
[  268.721758]  ? locks_remove_file+0x282/0x3d0
[  268.722529]  ? security_file_free+0xaa/0xd0
[  268.723224]  __fput+0x2be/0x770
[  268.723743]  task_work_run+0x10e/0x1b0
[  268.724428]  exit_to_usermode_loop+0x145/0x170
[  268.725172]  do_syscall_64+0x2d0/0x390
[  268.725786]  ? prepare_exit_to_usermode+0x17a/0x230
[  268.726580]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[  268.727413] RIP: 0033:0x414da7
[  268.728029] Code: 00 00 0f 05 48 3d 00 f0 ff ff 77 3f f3 c3 0f 1f 44 00 00 53 89 fb 48 83 ec 10 e8 f4 fb ff ff 89 df 89 c2 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 2b 89 d7 89 44 24 0c e8 36 fc ff ff 8b 44 24
[  268.731055] RSP: 002b:00007fff39d379d0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
[  268.732322] RAX: 0000000000000000 RBX: 0000000000000003 RCX: 0000000000414da7
[  268.733587] RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000003
[  268.734818] RBP: 00007fff39d37a3c R08: 0000000400000000 R09: 0000000400000000
[  268.736472] R10: 00007fff39d37910 R11: 0000000000000293 R12: 0000000000000001
[  268.737754] R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000003
[  268.738983] Dumping ftrace buffer:
[  268.739601]    (ftrace buffer empty)
[  268.740181] Kernel Offset: disabled
[  268.740770] Rebooting in 1 seconds..

Fixes: aba94548c9e4 ("IB/uverbs: Move the FD uobj type struct file allocation to alloc_commit")
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
---
 drivers/infiniband/core/rdma_core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/infiniband/core/rdma_core.c b/drivers/infiniband/core/rdma_core.c
index 3027cd2fb247..6d3ed7c6e19e 100644
--- a/drivers/infiniband/core/rdma_core.c
+++ b/drivers/infiniband/core/rdma_core.c
@@ -649,9 +649,6 @@ void rdma_alloc_commit_uobject(struct ib_uobject *uobj,
 {
 	struct ib_uverbs_file *ufile = attrs->ufile;
 
-	/* alloc_commit consumes the uobj kref */
-	uobj->uapi_object->type_class->alloc_commit(uobj);
-
 	/* kref is held so long as the uobj is on the uobj list. */
 	uverbs_uobject_get(uobj);
 	spin_lock_irq(&ufile->uobjects_lock);
@@ -661,6 +658,9 @@ void rdma_alloc_commit_uobject(struct ib_uobject *uobj,
 	/* matches atomic_set(-1) in alloc_uobj */
 	atomic_set(&uobj->usecnt, 0);
 
+	/* alloc_commit consumes the uobj kref */
+	uobj->uapi_object->type_class->alloc_commit(uobj);
+
 	/* Matches the down_read in rdma_alloc_begin_uobject */
 	up_read(&ufile->hw_destroy_rwsem);
 }
-- 
2.26.2