Re: [PATCH v3 5/8] proc/kcore: hold lock during read

From: Tetsuo Handa
Date: Tue Jul 24 2018 - 11:12:14 EST

On 2018/07/19 7:58, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@xxxxxx>
>
> Now that we're using an rwsem, we can hold it during the entirety of
> read_kcore() and have a common return path. This is preparation for the
> next change.
>
> Signed-off-by: Omar Sandoval <osandov@xxxxxx>
> ---
> fs/proc/kcore.c | 70 ++++++++++++++++++++++++++++---------------------
> 1 file changed, 40 insertions(+), 30 deletions(-)
>
> diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
> index 95aa988c5b5d..e317ac890871 100644
> --- a/fs/proc/kcore.c
> +++ b/fs/proc/kcore.c
> @@ -440,19 +440,18 @@ static ssize_t
> read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
> {
> char *buf = file->private_data;
> - ssize_t acc = 0;
> size_t size, tsz;
> size_t elf_buflen;
> int nphdr;
> unsigned long start;
> + size_t orig_buflen = buflen;
> + int ret = 0;
>
> down_read(&kclist_lock);

(...snipped...)

> +out:
> + up_write(&kclist_lock);

Oops. This needs to be up_read().

> + if (ret)
> + return ret;
> + return orig_buflen - buflen;
> }
>
[ 43.508922] ------------[ cut here ]------------
[ 43.509931] DEBUG_LOCKS_WARN_ON(sem->owner != get_current())
[ 43.509940] WARNING: CPU: 0 PID: 7933 at kernel/locking/rwsem.c:133 up_write+0x75/0x80
[ 43.512792] Modules linked in: pcspkr sg vmw_vmci i2c_piix4 sd_mod ata_generic pata_acpi vmwgfx drm_kms_helper syscopyarea ahci sysfillrect libahci sysimgblt fb_sys_fops mptspi ata_piix ttm scsi_transport_spi mptscsih drm e1000 mptbase libata i2c_core serio_raw ipv6 crc_ccitt
[ 43.517692] CPU: 0 PID: 7933 Comm: kexec Not tainted 4.18.0-rc6-next-20180724+ #715
[ 43.519237] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 05/19/2017
[ 43.521498] RIP: 0010:up_write+0x75/0x80
[ 43.522391] Code: 00 5b c3 e8 0d 03 3a 00 85 c0 74 d9 83 3d 6a e4 10 02 00 75 d0 48 c7 c6 c8 2f e0 81 48 c7 c7 a3 e3 de 81 31 c0 e8 fb 8d fa ff <0f> 0b eb b7 0f 1f 80 00 00 00 00 8b 05 42 3e 06 02 53 48 89 fb 85
[ 43.526253] RSP: 0018:ffffc90007ec7bc8 EFLAGS: 00010282
[ 43.527303] RAX: 0000000000000000 RBX: ffffffff8207b5e0 RCX: 0000000000000006
[ 43.528874] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88013ba15b70
[ 43.530496] RBP: ffffc90007ec7e28 R08: 0000000000000000 R09: 0000000000000001
[ 43.532007] R10: 0000000000000000 R11: 292928746e657272 R12: ffffffff8207b660
[ 43.533448] R13: 0000000000000000 R14: 0000000000000000 R15: 000000000000e000
[ 43.534969] FS: 00007fdd6e0c0740(0000) GS:ffff88013ba00000(0000) knlGS:0000000000000000
[ 43.536623] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 43.537943] CR2: 00000000017dc000 CR3: 00000001376b5006 CR4: 00000000001606f0
[ 43.539608] Call Trace:
[ 43.540154] read_kcore+0x81/0x630
[ 43.540932] proc_reg_read+0x34/0x60
[ 43.541722] __vfs_read+0x2e/0x160
[ 43.542450] vfs_read+0x84/0x130
[ 43.543166] ksys_read+0x50/0xc0
[ 43.543856] do_syscall_64+0x4f/0x1f0
[ 43.544684] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 43.545909] RIP: 0033:0x7fdd6d798c70
[ 43.546688] Code: 0b 31 c0 48 83 c4 08 e9 be fe ff ff 48 8d 3d 07 b9 09 00 e8 52 8a 02 00 66 90 83 3d 2d c3 2d 00 00 75 10 b8 00 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 4e cc 01 00 48 89 04 24
[ 43.550607] RSP: 002b:00007fffe5207428 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[ 43.552192] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fdd6d798c70
[ 43.553711] RDX: 0000000000010000 RSI: 00000000017cd840 RDI: 0000000000000004
[ 43.555240] RBP: 0000000000010000 R08: 0000000000000001 R09: 0000000000010000
[ 43.556779] R10: 0000000000000079 R11: 0000000000000246 R12: 0000000000000004
[ 43.558284] R13: 00000000017cd840 R14: 00007fffe52074d8 R15: 00007fffe52076c0
[ 43.559809] irq event stamp: 25471
[ 43.560597] hardirqs last enabled at (25471): [<ffffffff81800966>] restore_regs_and_return_to_kernel+0x0/0x2a
[ 43.562821] hardirqs last disabled at (25470): [<ffffffff81800fa6>] error_exit+0x6/0x20
[ 43.564515] softirqs last enabled at (24962): [<ffffffff81a001db>] __do_softirq+0x1db/0x48e
[ 43.566308] softirqs last disabled at (24955): [<ffffffff8107197d>] irq_exit+0xcd/0xe0
[ 43.567982] ---[ end trace 0140237dd1b1be70 ]---