Re: [PATCH v3 2/7] zram: fix double free backing device

[Sergey Senozhatsky]

On (11/27/18 14:54), Minchan Kim wrote:
> If blkdev_get fails, we shouldn't do blkdev_put. Otherwise,
> kernel emits below log. This patch fixes it.
> 
> [   31.073006] WARNING: CPU: 0 PID: 1893 at fs/block_dev.c:1828 blkdev_put+0x105/0x120
> [   31.075104] Modules linked in:
> [   31.075898] CPU: 0 PID: 1893 Comm: swapoff Not tainted 4.19.0+ #453
> [   31.077484] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> [   31.079589] RIP: 0010:blkdev_put+0x105/0x120
> [   31.080606] Code: 48 c7 80 a0 00 00 00 00 00 00 00 48 c7 c7 40 e7 40 96 e8 6e 47 73 00 48 8b bb e0 00 00 00 e9 2c ff ff ff 0f 0b e9 75 ff ff ff <0f> 0b e9 5a ff ff ff 48 c7 80 a0 00 00 00 00 00 00 00 eb 87 0f 1f
> [   31.085080] RSP: 0018:ffffb409005c7ed0 EFLAGS: 00010297
> [   31.086383] RAX: ffff9779fe5a8040 RBX: ffff9779fbc17300 RCX: 00000000b9fc37a4
> [   31.088105] RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffffffff9640e740
> [   31.089850] RBP: ffff9779fbc17318 R08: ffffffff95499a89 R09: 0000000000000004
> [   31.091201] R10: ffffb409005c7e50 R11: 7a9ef6088ff4d4a1 R12: 0000000000000083
> [   31.092276] R13: ffff9779fe607b98 R14: 0000000000000000 R15: ffff9779fe607a38
> [   31.093355] FS:  00007fc118d9b840(0000) GS:ffff9779fc600000(0000) knlGS:0000000000000000
> [   31.094582] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   31.095541] CR2: 00007fc11894b8dc CR3: 00000000339f6001 CR4: 0000000000160ef0
> [   31.096781] Call Trace:
> [   31.097212]  __x64_sys_swapoff+0x46d/0x490
> [   31.097914]  do_syscall_64+0x5a/0x190
> [   31.098550]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> [   31.099402] RIP: 0033:0x7fc11843ec27
> [   31.100013] Code: 73 01 c3 48 8b 0d 71 62 2c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 a8 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 41 62 2c 00 f7 d8 64 89 01 48
> [   31.103149] RSP: 002b:00007ffdf69be648 EFLAGS: 00000206 ORIG_RAX: 00000000000000a8
> [   31.104425] RAX: ffffffffffffffda RBX: 00000000011d98c0 RCX: 00007fc11843ec27
> [   31.105627] RDX: 0000000000000001 RSI: 0000000000000001 RDI: 00000000011d98c0
> [   31.106847] RBP: 0000000000000001 R08: 00007ffdf69be690 R09: 0000000000000001
> [   31.108038] R10: 00000000000002b1 R11: 0000000000000206 R12: 0000000000000001
> [   31.109231] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> [   31.110433] irq event stamp: 4466
> [   31.111001] hardirqs last  enabled at (4465): [<ffffffff953ebd43>] __free_pages_ok+0x1e3/0x490
> [   31.112437] hardirqs last disabled at (4466): [<ffffffff95201b7a>] trace_hardirqs_off_thunk+0x1a/0x1c
> [   31.113973] softirqs last  enabled at (3420): [<ffffffff95e00333>] __do_softirq+0x333/0x446
> [   31.115364] softirqs last disabled at (3407): [<ffffffff9527aee1>] irq_exit+0xd1/0xe0
> 
> Cc: stable@xxxxxxxxxxxxxxx # 4.14+
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>

Good catch.

Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>

	-ss