On 2021/09/06 3:11, Luis Chamberlain wrote:
> On Sat, Sep 04, 2021 at 11:49:06AM +0900, Tetsuo Handa wrote:
>> On 2021/09/04 10:39, Luis Chamberlain wrote:
>>> diff --git a/fs/block_dev.c b/fs/block_dev.c
>>> index 45df6cbccf12..81a4738910a8 100644
>>> --- a/fs/block_dev.c
>>> +++ b/fs/block_dev.c
>>> @@ -1144,10 +1144,13 @@ struct block_device *blkdev_get_no_open(dev_t dev)
>>> {
>>> struct block_device *bdev;
>>> struct inode *inode;
>>> + int ret;
>>>
>>> inode = ilookup(blockdev_superblock, dev);
>>> if (!inode) {
>>> - blk_request_module(dev);
>>> + ret = blk_request_module(dev);
>>> + if (ret)
>>> + return NULL;
>>
>> Since e.g. loop_add() from loop_probe() returns -EEXIST when /dev/loop$num already
>> exists (e.g. raced with ioctl(LOOP_CTL_ADD)), isn't unconditionally failing an over-failing?
>
> It's not clear to me how. What do we loose by capturing the failure on
> blk_request_module()?
>
We loose ability to handle concurrent request.
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 45df6cbccf12..9559c8aabc88 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -36,6 +36,7 @@
#include <linux/suspend.h>
#include "internal.h"
#include "../block/blk.h"
+#include <linux/debug_locks.h>
struct bdev_inode {
struct block_device bdev;
@@ -1147,7 +1148,11 @@ struct block_device *blkdev_get_no_open(dev_t dev)
inode = ilookup(blockdev_superblock, dev);
if (!inode) {
+ dump_stack();
+ debug_show_held_locks(current);
blk_request_module(dev);
+ if (!strcmp(current->comm, "cat"))
+ schedule_timeout_killable(10 * HZ);
inode = ilookup(blockdev_superblock, dev);
if (!inode)
return NULL;
Try "mknod /dev/loop$num b 7 $num" followed by concurrent "cat /dev/loop$num" requests.
[ 535.847823] [ T5261] CPU: 1 PID: 5261 Comm: cat Tainted: G E 5.14.0-next-20210903+ #3
[ 535.851419] [ T5261] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 02/27/2020
[ 535.855563] [ T5261] Call Trace:
[ 535.856746] [ T5261] dump_stack_lvl+0x79/0xbf
[ 535.858332] [ T5261] blkdev_get_no_open+0x86/0xe0
[ 535.860036] [ T5261] blkdev_get_by_dev+0x5f/0x540
[ 535.861747] [ T5261] ? block_ioctl+0x40/0x40
[ 535.863305] [ T5261] blkdev_open+0x58/0x90
[ 535.864865] [ T5261] do_dentry_open+0x144/0x3a0
[ 535.866538] [ T5261] path_openat+0xa57/0xda0
[ 535.868139] [ T5261] do_filp_open+0x9f/0x140
[ 535.869933] [ T5261] ? _raw_spin_unlock+0x1a/0x30
[ 535.871570] [ T5261] do_sys_openat2+0x71/0x150
[ 535.873195] [ T5261] __x64_sys_openat+0x78/0xa0
[ 535.874740] [ T5261] do_syscall_64+0x3d/0xb0
[ 535.876234] [ T5261] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 535.878428] [ T5261] RIP: 0033:0x7f6b997d28db
[ 535.879927] [ T5261] Code: 25 00 00 41 00 3d 00 00 41 00 74 4b 64 8b 04 25 18 00 00 00 85 c0 75 67 44 89 e2 48 89 ee bf 9c ff ff ff b8 01 01 00 00 0f 05 <48> 3d 00 f0 ff ff 0f 87 91 00 00 00 48 8b 4c 24 28 64 48 2b 0c 25
[ 535.886778] [ T5261] RSP: 002b:00007ffe8bdad880 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
[ 535.889727] [ T5261] RAX: ffffffffffffffda RBX: 000055f741e5b634 RCX: 00007f6b997d28db
[ 535.892466] [ T5261] RDX: 0000000000000000 RSI: 00007ffe8bdaf764 RDI: 00000000ffffff9c
[ 535.895226] [ T5261] RBP: 00007ffe8bdaf764 R08: 0000000000000001 R09: 0000000000000000
[ 535.898162] [ T5261] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
[ 535.900858] [ T5261] R13: 00007ffe8bdadb68 R14: 0000000000000000 R15: 0000000000020000
[ 535.903752] [ T5262] CPU: 2 PID: 5262 Comm: cat Tainted: G E 5.14.0-next-20210903+ #3
[ 535.904759] [ T5261] no locks held by cat/5261.
[ 535.906905] [ T5262] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 02/27/2020
[ 535.906908] [ T5262] Call Trace:
[ 535.906912] [ T5262] dump_stack_lvl+0x79/0xbf
[ 535.915279] [ T5262] blkdev_get_no_open+0x86/0xe0
[ 535.916942] [ T5262] blkdev_get_by_dev+0x5f/0x540
[ 535.918608] [ T5262] ? block_ioctl+0x40/0x40
[ 535.920250] [ T5262] blkdev_open+0x58/0x90
[ 535.921696] [ T5262] do_dentry_open+0x144/0x3a0
[ 535.923291] [ T5262] path_openat+0xa57/0xda0
[ 535.924816] [ T5262] do_filp_open+0x9f/0x140
[ 535.926359] [ T5262] ? _raw_spin_unlock+0x1a/0x30
[ 535.928030] [ T5262] do_sys_openat2+0x71/0x150
[ 535.929600] [ T5262] __x64_sys_openat+0x78/0xa0
[ 535.931215] [ T5262] do_syscall_64+0x3d/0xb0
[ 535.932768] [ T5262] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 535.934817] [ T5262] RIP: 0033:0x7efe3a0aa8db
[ 535.936354] [ T5262] Code: 25 00 00 41 00 3d 00 00 41 00 74 4b 64 8b 04 25 18 00 00 00 85 c0 75 67 44 89 e2 48 89 ee bf 9c ff ff ff b8 01 01 00 00 0f 05 <48> 3d 00 f0 ff ff 0f 87 91 00 00 00 48 8b 4c 24 28 64 48 2b 0c 25
[ 535.943021] [ T5262] RSP: 002b:00007ffe1697dfb0 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
[ 535.945883] [ T5262] RAX: ffffffffffffffda RBX: 000055982a4e1634 RCX: 00007efe3a0aa8db
[ 535.948580] [ T5262] RDX: 0000000000000000 RSI: 00007ffe1697e764 RDI: 00000000ffffff9c
[ 535.951298] [ T5262] RBP: 00007ffe1697e764 R08: 0000000000000001 R09: 0000000000000000
[ 535.954064] [ T5262] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
[ 535.956789] [ T5262] R13: 00007ffe1697e298 R14: 0000000000000000 R15: 0000000000020000
[ 535.959522] [ T5263] CPU: 0 PID: 5263 Comm: cat Tainted: G E 5.14.0-next-20210903+ #3
[ 535.962995] [ T5263] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 02/27/2020
[ 535.965787] [ T5262] no locks held by cat/5262.
[ 535.966998] [ T5263] Call Trace:
[ 535.970068] [ T5263] dump_stack_lvl+0x79/0xbf
[ 535.971572] [ T5263] blkdev_get_no_open+0x86/0xe0
[ 535.973199] [ T5263] blkdev_get_by_dev+0x5f/0x540
[ 535.974893] [ T5263] ? block_ioctl+0x40/0x40
[ 535.976364] [ T5263] blkdev_open+0x58/0x90
[ 535.977781] [ T5263] do_dentry_open+0x144/0x3a0
[ 535.979378] [ T5263] path_openat+0xa57/0xda0
[ 535.980882] [ T5263] do_filp_open+0x9f/0x140
[ 535.982333] [ T5263] ? _raw_spin_unlock+0x1a/0x30
[ 535.984002] [ T5263] do_sys_openat2+0x71/0x150
[ 535.985554] [ T5263] __x64_sys_openat+0x78/0xa0
[ 535.987232] [ T5263] do_syscall_64+0x3d/0xb0
[ 535.988790] [ T5263] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 535.990804] [ T5263] RIP: 0033:0x7ff84ab408db
[ 535.992275] [ T5263] Code: 25 00 00 41 00 3d 00 00 41 00 74 4b 64 8b 04 25 18 00 00 00 85 c0 75 67 44 89 e2 48 89 ee bf 9c ff ff ff b8 01 01 00 00 0f 05 <48> 3d 00 f0 ff ff 0f 87 91 00 00 00 48 8b 4c 24 28 64 48 2b 0c 25
[ 535.998888] [ T5263] RSP: 002b:00007ffda9b89a70 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
[ 536.001628] [ T5263] RAX: ffffffffffffffda RBX: 000055626f376634 RCX: 00007ff84ab408db
[ 536.004350] [ T5263] RDX: 0000000000000000 RSI: 00007ffda9b8a764 RDI: 00000000ffffff9c
[ 536.007009] [ T5263] RBP: 00007ffda9b8a764 R08: 0000000000000001 R09: 0000000000000000
[ 536.009753] [ T5263] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
[ 536.012493] [ T5263] R13: 00007ffda9b89d58 R14: 0000000000000000 R15: 0000000000020000
[ 536.015854] [ T5263] no locks held by cat/5263.
If blk_request_module() does not ignore -EEXIST error, only the first open() request would succeed
because loop_add() returns 0 and all other concurrent requests would fail because loop_add() returns -EEXIST.
Actually, blk_request_module() failures should be ignored, for subsequent ilookup() will
fail if blk_request_module() failed to create the requested block device.
