Freezing and thawing are separate system calls, task which is supposed
to thaw filesystem/superblock can disappear due to crash or not thaw
due to a bug. Record at least task name (we can't take task_struct
reference) to make support engineer's life easier.
Hopefully 16 bytes per superblock isn't much.
P.S.: Cc'ing GFS2 people just in case they want to correct
my understanding of GFS2 having async freeze code.
Signed-off-by: Alexey Dobriyan <[email protected]>
---
fs/ioctl.c | 22 ++++++++++++++++------
fs/super.c | 2 ++
include/linux/fs.h | 2 ++
3 files changed, 20 insertions(+), 6 deletions(-)
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -518,6 +518,7 @@ static int ioctl_fioasync(unsigned int fd, struct file *filp,
static int ioctl_fsfreeze(struct file *filp)
{
struct super_block *sb = file_inode(filp)->i_sb;
+ int rv;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
@@ -527,22 +528,31 @@ static int ioctl_fsfreeze(struct file *filp)
return -EOPNOTSUPP;
/* Freeze */
- if (sb->s_op->freeze_super)
- return sb->s_op->freeze_super(sb);
- return freeze_super(sb);
+ if (sb->s_op->freeze_super) {
+ rv = sb->s_op->freeze_super(sb);
+ if (rv == 0)
+ get_task_comm(sb->s_writers.freeze_comm, current);
+ } else
+ rv = freeze_super(sb);
+ return rv;
}
static int ioctl_fsthaw(struct file *filp)
{
struct super_block *sb = file_inode(filp)->i_sb;
+ int rv;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
/* Thaw */
- if (sb->s_op->thaw_super)
- return sb->s_op->thaw_super(sb);
- return thaw_super(sb);
+ if (sb->s_op->thaw_super) {
+ rv = sb->s_op->thaw_super(sb);
+ if (rv == 0)
+ memset(sb->s_writers.freeze_comm, 0, TASK_COMM_LEN);
+ } else
+ rv = thaw_super(sb);
+ return rv;
}
/*
--- a/fs/super.c
+++ b/fs/super.c
@@ -1355,6 +1355,7 @@ int freeze_super(struct super_block *sb)
* sees write activity when frozen is set to SB_FREEZE_COMPLETE.
*/
sb->s_writers.frozen = SB_FREEZE_COMPLETE;
+ get_task_comm(sb->s_writers.freeze_comm, current);
up_write(&sb->s_umount);
return 0;
}
@@ -1391,6 +1392,7 @@ int thaw_super(struct super_block *sb)
out:
sb->s_writers.frozen = SB_UNFROZEN;
+ memset(sb->s_writers.freeze_comm, 0, TASK_COMM_LEN);
smp_wmb();
wake_up(&sb->s_writers.wait_unfrozen);
deactivate_locked_super(sb);
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1221,6 +1221,8 @@ struct sb_writers {
int frozen; /* Is sb frozen? */
wait_queue_head_t wait_unfrozen; /* queue for waiting for
sb to be thawed */
+ /* who froze superblock */
+ char freeze_comm[16];
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map lock_map[SB_FREEZE_LEVELS];
#endif
On Sat 14-02-15 21:55:24, Alexey Dobriyan wrote:
> Freezing and thawing are separate system calls, task which is supposed
> to thaw filesystem/superblock can disappear due to crash or not thaw
> due to a bug. Record at least task name (we can't take task_struct
> reference) to make support engineer's life easier.
>
> Hopefully 16 bytes per superblock isn't much.
>
> P.S.: Cc'ing GFS2 people just in case they want to correct
> my understanding of GFS2 having async freeze code.
>
> Signed-off-by: Alexey Dobriyan <[email protected]>
Hum, and when do you show the task name? Or do you expect that customer
takes a crashdump and support just finds it in memory?
> ---
>
> fs/ioctl.c | 22 ++++++++++++++++------
> fs/super.c | 2 ++
> include/linux/fs.h | 2 ++
> 3 files changed, 20 insertions(+), 6 deletions(-)
>
> --- a/fs/ioctl.c
> +++ b/fs/ioctl.c
> @@ -518,6 +518,7 @@ static int ioctl_fioasync(unsigned int fd, struct file *filp,
> static int ioctl_fsfreeze(struct file *filp)
> {
> struct super_block *sb = file_inode(filp)->i_sb;
> + int rv;
>
> if (!capable(CAP_SYS_ADMIN))
> return -EPERM;
> @@ -527,22 +528,31 @@ static int ioctl_fsfreeze(struct file *filp)
> return -EOPNOTSUPP;
>
> /* Freeze */
> - if (sb->s_op->freeze_super)
> - return sb->s_op->freeze_super(sb);
> - return freeze_super(sb);
> + if (sb->s_op->freeze_super) {
> + rv = sb->s_op->freeze_super(sb);
> + if (rv == 0)
> + get_task_comm(sb->s_writers.freeze_comm, current);
> + } else
> + rv = freeze_super(sb);
> + return rv;
Why don't you just set the name in ioctl_fsfreeze() in both cases?
Also you seem to be missing freezing / thawing in freeze/thaw_bdev()
functions.
> }
>
> static int ioctl_fsthaw(struct file *filp)
> {
> struct super_block *sb = file_inode(filp)->i_sb;
> + int rv;
>
> if (!capable(CAP_SYS_ADMIN))
> return -EPERM;
>
> /* Thaw */
> - if (sb->s_op->thaw_super)
> - return sb->s_op->thaw_super(sb);
> - return thaw_super(sb);
> + if (sb->s_op->thaw_super) {
> + rv = sb->s_op->thaw_super(sb);
> + if (rv == 0)
> + memset(sb->s_writers.freeze_comm, 0, TASK_COMM_LEN);
> + } else
> + rv = thaw_super(sb);
> + return rv;
> }
>
> /*
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -1355,6 +1355,7 @@ int freeze_super(struct super_block *sb)
> * sees write activity when frozen is set to SB_FREEZE_COMPLETE.
> */
> sb->s_writers.frozen = SB_FREEZE_COMPLETE;
> + get_task_comm(sb->s_writers.freeze_comm, current);
> up_write(&sb->s_umount);
> return 0;
> }
> @@ -1391,6 +1392,7 @@ int thaw_super(struct super_block *sb)
>
> out:
> sb->s_writers.frozen = SB_UNFROZEN;
> + memset(sb->s_writers.freeze_comm, 0, TASK_COMM_LEN);
> smp_wmb();
> wake_up(&sb->s_writers.wait_unfrozen);
> deactivate_locked_super(sb);
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1221,6 +1221,8 @@ struct sb_writers {
> int frozen; /* Is sb frozen? */
> wait_queue_head_t wait_unfrozen; /* queue for waiting for
> sb to be thawed */
> + /* who froze superblock */
> + char freeze_comm[16];
Here should be TASK_COMM_LEN, shouldn't it?
Honza
--
Jan Kara <[email protected]>
SUSE Labs, CR
On Mon, Feb 16, 2015 at 10:38:52AM +0100, Jan Kara wrote:
> On Sat 14-02-15 21:55:24, Alexey Dobriyan wrote:
> > Freezing and thawing are separate system calls, task which is supposed
> > to thaw filesystem/superblock can disappear due to crash or not thaw
> > due to a bug. Record at least task name (we can't take task_struct
> > reference) to make support engineer's life easier.
> >
> > Hopefully 16 bytes per superblock isn't much.
> >
> > P.S.: Cc'ing GFS2 people just in case they want to correct
> > my understanding of GFS2 having async freeze code.
> >
> > Signed-off-by: Alexey Dobriyan <[email protected]>
> Hum, and when do you show the task name? Or do you expect that customer
> takes a crashdump and support just finds it in memory?
Yeah, having at least something in crashdump is fine.
> > --- a/fs/ioctl.c
> > +++ b/fs/ioctl.c
> > @@ -518,6 +518,7 @@ static int ioctl_fioasync(unsigned int fd, struct file *filp,
> > static int ioctl_fsfreeze(struct file *filp)
> > {
> > struct super_block *sb = file_inode(filp)->i_sb;
> > + int rv;
> >
> > if (!capable(CAP_SYS_ADMIN))
> > return -EPERM;
> > @@ -527,22 +528,31 @@ static int ioctl_fsfreeze(struct file *filp)
> > return -EOPNOTSUPP;
> >
> > /* Freeze */
> > - if (sb->s_op->freeze_super)
> > - return sb->s_op->freeze_super(sb);
> > - return freeze_super(sb);
> > + if (sb->s_op->freeze_super) {
> > + rv = sb->s_op->freeze_super(sb);
> > + if (rv == 0)
> > + get_task_comm(sb->s_writers.freeze_comm, current);
> > + } else
> > + rv = freeze_super(sb);
> > + return rv;
> Why don't you just set the name in ioctl_fsfreeze() in both cases?
There are users of freeze_super() in GFS2 unless I'm misreading code.
> Also you seem to be missing freezing / thawing in freeze/thaw_bdev()
> functions.
You are correct. Resending patch (blockdev freezing tested with XFS).
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -1221,6 +1221,8 @@ struct sb_writers {
> > int frozen; /* Is sb frozen? */
> > wait_queue_head_t wait_unfrozen; /* queue for waiting for
> > sb to be thawed */
> > + /* who froze superblock */
> > + char freeze_comm[16];
> Here should be TASK_COMM_LEN, shouldn't it?
It will pull sched.h, dunno if we care about headers anymore.
Alexey
Freezing and thawing are separate system calls, task which is supposed
to thaw filesystem/superblock can disappear due to crash or not thaw
due to a bug. Record at least task name (we can't take task_struct
reference) to make support engineer's life easier.
Hopefully 16 bytes per superblock isn't much.
Signed-off-by: Alexey Dobriyan <[email protected]>
---
fs/block_dev.c | 12 ++++++++----
fs/ioctl.c | 22 ++++++++++++++++------
fs/super.c | 2 ++
include/linux/fs.h | 2 ++
4 files changed, 28 insertions(+), 10 deletions(-)
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -227,9 +227,11 @@ struct super_block *freeze_bdev(struct block_device *bdev)
sb = get_active_super(bdev);
if (!sb)
goto out;
- if (sb->s_op->freeze_super)
+ if (sb->s_op->freeze_super) {
error = sb->s_op->freeze_super(sb);
- else
+ if (error == 0)
+ get_task_comm(sb->s_writers.freeze_comm, current);
+ } else
error = freeze_super(sb);
if (error) {
deactivate_super(sb);
@@ -267,9 +269,11 @@ int thaw_bdev(struct block_device *bdev, struct super_block *sb)
if (!sb)
goto out;
- if (sb->s_op->thaw_super)
+ if (sb->s_op->thaw_super) {
error = sb->s_op->thaw_super(sb);
- else
+ if (error == 0)
+ memset(sb->s_writers.freeze_comm, 0, TASK_COMM_LEN);
+ } else
error = thaw_super(sb);
if (error) {
bdev->bd_fsfreeze_count++;
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -518,6 +518,7 @@ static int ioctl_fioasync(unsigned int fd, struct file *filp,
static int ioctl_fsfreeze(struct file *filp)
{
struct super_block *sb = file_inode(filp)->i_sb;
+ int rv;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
@@ -527,22 +528,31 @@ static int ioctl_fsfreeze(struct file *filp)
return -EOPNOTSUPP;
/* Freeze */
- if (sb->s_op->freeze_super)
- return sb->s_op->freeze_super(sb);
- return freeze_super(sb);
+ if (sb->s_op->freeze_super) {
+ rv = sb->s_op->freeze_super(sb);
+ if (rv == 0)
+ get_task_comm(sb->s_writers.freeze_comm, current);
+ } else
+ rv = freeze_super(sb);
+ return rv;
}
static int ioctl_fsthaw(struct file *filp)
{
struct super_block *sb = file_inode(filp)->i_sb;
+ int rv;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
/* Thaw */
- if (sb->s_op->thaw_super)
- return sb->s_op->thaw_super(sb);
- return thaw_super(sb);
+ if (sb->s_op->thaw_super) {
+ rv = sb->s_op->thaw_super(sb);
+ if (rv == 0)
+ memset(sb->s_writers.freeze_comm, 0, TASK_COMM_LEN);
+ } else
+ rv = thaw_super(sb);
+ return rv;
}
/*
--- a/fs/super.c
+++ b/fs/super.c
@@ -1355,6 +1355,7 @@ int freeze_super(struct super_block *sb)
* sees write activity when frozen is set to SB_FREEZE_COMPLETE.
*/
sb->s_writers.frozen = SB_FREEZE_COMPLETE;
+ get_task_comm(sb->s_writers.freeze_comm, current);
up_write(&sb->s_umount);
return 0;
}
@@ -1391,6 +1392,7 @@ int thaw_super(struct super_block *sb)
out:
sb->s_writers.frozen = SB_UNFROZEN;
+ memset(sb->s_writers.freeze_comm, 0, TASK_COMM_LEN);
smp_wmb();
wake_up(&sb->s_writers.wait_unfrozen);
deactivate_locked_super(sb);
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1221,6 +1221,8 @@ struct sb_writers {
int frozen; /* Is sb frozen? */
wait_queue_head_t wait_unfrozen; /* queue for waiting for
sb to be thawed */
+ /* who froze superblock and forgot to thaw it */
+ char freeze_comm[16];
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map lock_map[SB_FREEZE_LEVELS];
#endif
On Wed 18-02-15 10:34:55, Alexey Dobriyan wrote:
> On Mon, Feb 16, 2015 at 10:38:52AM +0100, Jan Kara wrote:
> > On Sat 14-02-15 21:55:24, Alexey Dobriyan wrote:
> > > Freezing and thawing are separate system calls, task which is supposed
> > > to thaw filesystem/superblock can disappear due to crash or not thaw
> > > due to a bug. Record at least task name (we can't take task_struct
> > > reference) to make support engineer's life easier.
> > >
> > > Hopefully 16 bytes per superblock isn't much.
> > >
> > > P.S.: Cc'ing GFS2 people just in case they want to correct
> > > my understanding of GFS2 having async freeze code.
> > >
> > > Signed-off-by: Alexey Dobriyan <[email protected]>
> > Hum, and when do you show the task name? Or do you expect that customer
> > takes a crashdump and support just finds it in memory?
>
> Yeah, having at least something in crashdump is fine.
OK, then comment about this at freeze_comm[] definition so that it's
clear it isn't just set-but-never-read field.
> > > --- a/fs/ioctl.c
> > > +++ b/fs/ioctl.c
> > > @@ -518,6 +518,7 @@ static int ioctl_fioasync(unsigned int fd, struct file *filp,
> > > static int ioctl_fsfreeze(struct file *filp)
> > > {
> > > struct super_block *sb = file_inode(filp)->i_sb;
> > > + int rv;
> > >
> > > if (!capable(CAP_SYS_ADMIN))
> > > return -EPERM;
> > > @@ -527,22 +528,31 @@ static int ioctl_fsfreeze(struct file *filp)
> > > return -EOPNOTSUPP;
> > >
> > > /* Freeze */
> > > - if (sb->s_op->freeze_super)
> > > - return sb->s_op->freeze_super(sb);
> > > - return freeze_super(sb);
> > > + if (sb->s_op->freeze_super) {
> > > + rv = sb->s_op->freeze_super(sb);
> > > + if (rv == 0)
> > > + get_task_comm(sb->s_writers.freeze_comm, current);
> > > + } else
> > > + rv = freeze_super(sb);
> > > + return rv;
> > Why don't you just set the name in ioctl_fsfreeze() in both cases?
>
> There are users of freeze_super() in GFS2 unless I'm misreading code.
Yes, there are. The call in fs/gfs2/glops.c is in a call path from
->freeze_super() handler for GFS2 so that one is handled in
ioctl_fsfreeze() anyway. The call in fs/gfs2/sys.c is a way to freeze
filesystem via sysfs (dunno why GFS2 has to invent its own thing and ioctl
isn't enough). Steven? So having the logic in ioctl_fsfreeze(),
freeze_bdev() and freeze_store() in gfs2 seems to be enough.
> > Also you seem to be missing freezing / thawing in freeze/thaw_bdev()
> > functions.
>
> You are correct. Resending patch (blockdev freezing tested with XFS).
>
> > > --- a/include/linux/fs.h
> > > +++ b/include/linux/fs.h
> > > @@ -1221,6 +1221,8 @@ struct sb_writers {
> > > int frozen; /* Is sb frozen? */
> > > wait_queue_head_t wait_unfrozen; /* queue for waiting for
> > > sb to be thawed */
> > > + /* who froze superblock */
> > > + char freeze_comm[16];
> > Here should be TASK_COMM_LEN, shouldn't it?
>
> It will pull sched.h, dunno if we care about headers anymore.
That's not ideal but IMHO better than having the value hardcoded here.
That is pretty fragile - i.e. think what happens when someone decides to
increase TASK_COMM_LEN...
Honza
--
Jan Kara <[email protected]>
SUSE Labs, CR
Hi,
On 18/02/15 09:13, Jan Kara wrote:
> On Wed 18-02-15 10:34:55, Alexey Dobriyan wrote:
>> On Mon, Feb 16, 2015 at 10:38:52AM +0100, Jan Kara wrote:
>>> On Sat 14-02-15 21:55:24, Alexey Dobriyan wrote:
>>>> Freezing and thawing are separate system calls, task which is supposed
>>>> to thaw filesystem/superblock can disappear due to crash or not thaw
>>>> due to a bug. Record at least task name (we can't take task_struct
>>>> reference) to make support engineer's life easier.
>>>>
>>>> Hopefully 16 bytes per superblock isn't much.
>>>>
>>>> P.S.: Cc'ing GFS2 people just in case they want to correct
>>>> my understanding of GFS2 having async freeze code.
>>>>
>>>> Signed-off-by: Alexey Dobriyan <[email protected]>
>>> Hum, and when do you show the task name? Or do you expect that customer
>>> takes a crashdump and support just finds it in memory?
>> Yeah, having at least something in crashdump is fine.
> OK, then comment about this at freeze_comm[] definition so that it's
> clear it isn't just set-but-never-read field.
>
>>>> --- a/fs/ioctl.c
>>>> +++ b/fs/ioctl.c
>>>> @@ -518,6 +518,7 @@ static int ioctl_fioasync(unsigned int fd, struct file *filp,
>>>> static int ioctl_fsfreeze(struct file *filp)
>>>> {
>>>> struct super_block *sb = file_inode(filp)->i_sb;
>>>> + int rv;
>>>>
>>>> if (!capable(CAP_SYS_ADMIN))
>>>> return -EPERM;
>>>> @@ -527,22 +528,31 @@ static int ioctl_fsfreeze(struct file *filp)
>>>> return -EOPNOTSUPP;
>>>>
>>>> /* Freeze */
>>>> - if (sb->s_op->freeze_super)
>>>> - return sb->s_op->freeze_super(sb);
>>>> - return freeze_super(sb);
>>>> + if (sb->s_op->freeze_super) {
>>>> + rv = sb->s_op->freeze_super(sb);
>>>> + if (rv == 0)
>>>> + get_task_comm(sb->s_writers.freeze_comm, current);
>>>> + } else
>>>> + rv = freeze_super(sb);
>>>> + return rv;
>>> Why don't you just set the name in ioctl_fsfreeze() in both cases?
>> There are users of freeze_super() in GFS2 unless I'm misreading code.
> Yes, there are. The call in fs/gfs2/glops.c is in a call path from
> ->freeze_super() handler for GFS2 so that one is handled in
> ioctl_fsfreeze() anyway. The call in fs/gfs2/sys.c is a way to freeze
> filesystem via sysfs (dunno why GFS2 has to invent its own thing and ioctl
> isn't enough). Steven? So having the logic in ioctl_fsfreeze(),
> freeze_bdev() and freeze_store() in gfs2 seems to be enough.
>
The sysfs freeze thing is historical and strongly deprecated - I hope
that we may be able to remove it one day,
Steve.
On Wed, Feb 18, 2015 at 12:13 PM, Jan Kara <[email protected]> wrote:
> On Wed 18-02-15 10:34:55, Alexey Dobriyan wrote:
>> On Mon, Feb 16, 2015 at 10:38:52AM +0100, Jan Kara wrote:
>> > On Sat 14-02-15 21:55:24, Alexey Dobriyan wrote:
>> > > Freezing and thawing are separate system calls, task which is supposed
>> > > to thaw filesystem/superblock can disappear due to crash or not thaw
>> > > due to a bug. Record at least task name (we can't take task_struct
>> > > reference) to make support engineer's life easier.
>> > >
>> > > Hopefully 16 bytes per superblock isn't much.
>> > >
>> > > P.S.: Cc'ing GFS2 people just in case they want to correct
>> > > my understanding of GFS2 having async freeze code.
>> > >
>> > > Signed-off-by: Alexey Dobriyan <[email protected]>
>> > Hum, and when do you show the task name? Or do you expect that customer
>> > takes a crashdump and support just finds it in memory?
>>
>> Yeah, having at least something in crashdump is fine.
> OK, then comment about this at freeze_comm[] definition so that it's
> clear it isn't just set-but-never-read field.
OK.
>> > > --- a/fs/ioctl.c
>> > > +++ b/fs/ioctl.c
>> > > @@ -518,6 +518,7 @@ static int ioctl_fioasync(unsigned int fd, struct file *filp,
>> > > static int ioctl_fsfreeze(struct file *filp)
>> > > {
>> > > struct super_block *sb = file_inode(filp)->i_sb;
>> > > + int rv;
>> > >
>> > > if (!capable(CAP_SYS_ADMIN))
>> > > return -EPERM;
>> > > @@ -527,22 +528,31 @@ static int ioctl_fsfreeze(struct file *filp)
>> > > return -EOPNOTSUPP;
>> > >
>> > > /* Freeze */
>> > > - if (sb->s_op->freeze_super)
>> > > - return sb->s_op->freeze_super(sb);
>> > > - return freeze_super(sb);
>> > > + if (sb->s_op->freeze_super) {
>> > > + rv = sb->s_op->freeze_super(sb);
>> > > + if (rv == 0)
>> > > + get_task_comm(sb->s_writers.freeze_comm, current);
>> > > + } else
>> > > + rv = freeze_super(sb);
>> > > + return rv;
>> > Why don't you just set the name in ioctl_fsfreeze() in both cases?
>>
>> There are users of freeze_super() in GFS2 unless I'm misreading code.
> Yes, there are. The call in fs/gfs2/glops.c is in a call path from
> ->freeze_super() handler for GFS2 so that one is handled in
> ioctl_fsfreeze() anyway. The call in fs/gfs2/sys.c is a way to freeze
> filesystem via sysfs (dunno why GFS2 has to invent its own thing and ioctl
> isn't enough). Steven? So having the logic in ioctl_fsfreeze(),
> freeze_bdev() and freeze_store() in gfs2 seems to be enough.
Jan, my logic is as follows.
Recording freezer task name is not filesystem/device specific and
thus should be done in generic code. So no changes in GFS2.
freeze_super() is generic counterpart to filesystem/device
specific ->freeze_super() hook, look how they are paired.
It should recore freezer task name, so any future user
will not forget to do the same.
So it's in ioctl_fsfreeze(), freeze_bdev() and freeze_super().
>> > > --- a/include/linux/fs.h
>> > > +++ b/include/linux/fs.h
>> > > @@ -1221,6 +1221,8 @@ struct sb_writers {
>> > > int frozen; /* Is sb frozen? */
>> > > wait_queue_head_t wait_unfrozen; /* queue for waiting for
>> > > sb to be thawed */
>> > > + /* who froze superblock */
>> > > + char freeze_comm[16];
>> > Here should be TASK_COMM_LEN, shouldn't it?
>>
>> It will pull sched.h, dunno if we care about headers anymore.
> That's not ideal but IMHO better than having the value hardcoded here.
> That is pretty fragile - i.e. think what happens when someone decides to
> increase TASK_COMM_LEN...
TASK_COMM_LEN is userspace ABI via at least prctl(PR_SET_NAME).
I can formally move it to include/uapi/linux/sched.h.
This allows to not drag sched.h into fs.h for one tiny define.
Alexey
On Fri 20-02-15 14:42:29, Alexey Dobriyan wrote:
> On Wed, Feb 18, 2015 at 12:13 PM, Jan Kara <[email protected]> wrote:
> >> > > --- a/fs/ioctl.c
> >> > > +++ b/fs/ioctl.c
> >> > > @@ -518,6 +518,7 @@ static int ioctl_fioasync(unsigned int fd, struct file *filp,
> >> > > static int ioctl_fsfreeze(struct file *filp)
> >> > > {
> >> > > struct super_block *sb = file_inode(filp)->i_sb;
> >> > > + int rv;
> >> > >
> >> > > if (!capable(CAP_SYS_ADMIN))
> >> > > return -EPERM;
> >> > > @@ -527,22 +528,31 @@ static int ioctl_fsfreeze(struct file *filp)
> >> > > return -EOPNOTSUPP;
> >> > >
> >> > > /* Freeze */
> >> > > - if (sb->s_op->freeze_super)
> >> > > - return sb->s_op->freeze_super(sb);
> >> > > - return freeze_super(sb);
> >> > > + if (sb->s_op->freeze_super) {
> >> > > + rv = sb->s_op->freeze_super(sb);
> >> > > + if (rv == 0)
> >> > > + get_task_comm(sb->s_writers.freeze_comm, current);
> >> > > + } else
> >> > > + rv = freeze_super(sb);
> >> > > + return rv;
> >> > Why don't you just set the name in ioctl_fsfreeze() in both cases?
> >>
> >> There are users of freeze_super() in GFS2 unless I'm misreading code.
> > Yes, there are. The call in fs/gfs2/glops.c is in a call path from
> > ->freeze_super() handler for GFS2 so that one is handled in
> > ioctl_fsfreeze() anyway. The call in fs/gfs2/sys.c is a way to freeze
> > filesystem via sysfs (dunno why GFS2 has to invent its own thing and ioctl
> > isn't enough). Steven? So having the logic in ioctl_fsfreeze(),
> > freeze_bdev() and freeze_store() in gfs2 seems to be enough.
>
> Jan, my logic is as follows.
>
> Recording freezer task name is not filesystem/device specific and
> thus should be done in generic code. So no changes in GFS2.
>
> freeze_super() is generic counterpart to filesystem/device
> specific ->freeze_super() hook, look how they are paired.
> It should recore freezer task name, so any future user
> will not forget to do the same.
>
> So it's in ioctl_fsfreeze(), freeze_bdev() and freeze_super().
Well, but this stores the name in two different levels - once in the top
level (ioctl_fsfreeze(), freeze_bdev()) and once in a place called from
there (freeze_super()). That just seems wrong to me. You can just record
the frozen process in freeze_super() and mandate that if someone manages to
freeze the fs without calling freeze_super() from his ->freeze_super()
handler (currently there isn't such filesystem), he is also responsible for
setting freezer name... Hmm?
> >> > > --- a/include/linux/fs.h
> >> > > +++ b/include/linux/fs.h
> >> > > @@ -1221,6 +1221,8 @@ struct sb_writers {
> >> > > int frozen; /* Is sb frozen? */
> >> > > wait_queue_head_t wait_unfrozen; /* queue for waiting for
> >> > > sb to be thawed */
> >> > > + /* who froze superblock */
> >> > > + char freeze_comm[16];
> >> > Here should be TASK_COMM_LEN, shouldn't it?
> >>
> >> It will pull sched.h, dunno if we care about headers anymore.
> > That's not ideal but IMHO better than having the value hardcoded here.
> > That is pretty fragile - i.e. think what happens when someone decides to
> > increase TASK_COMM_LEN...
>
> TASK_COMM_LEN is userspace ABI via at least prctl(PR_SET_NAME).
> I can formally move it to include/uapi/linux/sched.h.
> This allows to not drag sched.h into fs.h for one tiny define.
OK, moving the definition would be preferable to me (and IMO also a
cleanup).
Honza
--
Jan Kara <[email protected]>
SUSE Labs, CR
On Fri, Feb 20, 2015 at 01:15:22PM +0100, Jan Kara wrote:
> On Fri 20-02-15 14:42:29, Alexey Dobriyan wrote:
> > On Wed, Feb 18, 2015 at 12:13 PM, Jan Kara <[email protected]> wrote:
> > >> > > --- a/fs/ioctl.c
> > >> > > +++ b/fs/ioctl.c
> > >> > > @@ -518,6 +518,7 @@ static int ioctl_fioasync(unsigned int fd, struct file *filp,
> > >> > > static int ioctl_fsfreeze(struct file *filp)
> > >> > > {
> > >> > > struct super_block *sb = file_inode(filp)->i_sb;
> > >> > > + int rv;
> > >> > >
> > >> > > if (!capable(CAP_SYS_ADMIN))
> > >> > > return -EPERM;
> > >> > > @@ -527,22 +528,31 @@ static int ioctl_fsfreeze(struct file *filp)
> > >> > > return -EOPNOTSUPP;
> > >> > >
> > >> > > /* Freeze */
> > >> > > - if (sb->s_op->freeze_super)
> > >> > > - return sb->s_op->freeze_super(sb);
> > >> > > - return freeze_super(sb);
> > >> > > + if (sb->s_op->freeze_super) {
> > >> > > + rv = sb->s_op->freeze_super(sb);
> > >> > > + if (rv == 0)
> > >> > > + get_task_comm(sb->s_writers.freeze_comm, current);
> > >> > > + } else
> > >> > > + rv = freeze_super(sb);
> > >> > > + return rv;
> > >> > Why don't you just set the name in ioctl_fsfreeze() in both cases?
> > >>
> > >> There are users of freeze_super() in GFS2 unless I'm misreading code.
> > > Yes, there are. The call in fs/gfs2/glops.c is in a call path from
> > > ->freeze_super() handler for GFS2 so that one is handled in
> > > ioctl_fsfreeze() anyway. The call in fs/gfs2/sys.c is a way to freeze
> > > filesystem via sysfs (dunno why GFS2 has to invent its own thing and ioctl
> > > isn't enough). Steven? So having the logic in ioctl_fsfreeze(),
> > > freeze_bdev() and freeze_store() in gfs2 seems to be enough.
> >
> > Jan, my logic is as follows.
> >
> > Recording freezer task name is not filesystem/device specific and
> > thus should be done in generic code. So no changes in GFS2.
> >
> > freeze_super() is generic counterpart to filesystem/device
> > specific ->freeze_super() hook, look how they are paired.
> > It should recore freezer task name, so any future user
> > will not forget to do the same.
> >
> > So it's in ioctl_fsfreeze(), freeze_bdev() and freeze_super().
> Well, but this stores the name in two different levels - once in the top
> level (ioctl_fsfreeze(), freeze_bdev()) and once in a place called from
> there (freeze_super()). That just seems wrong to me. You can just record
> the frozen process in freeze_super() and mandate that if someone manages to
> freeze the fs without calling freeze_super() from his ->freeze_super()
> handler (currently there isn't such filesystem), he is also responsible for
> setting freezer name... Hmm?
Jan I understand you. But I find stranger that GFS will have to record
freezer name.
I'm sending v3, hopefully final.
> > >> > > --- a/include/linux/fs.h
> > >> > > +++ b/include/linux/fs.h
> > >> > > @@ -1221,6 +1221,8 @@ struct sb_writers {
> > >> > > int frozen; /* Is sb frozen? */
> > >> > > wait_queue_head_t wait_unfrozen; /* queue for waiting for
> > >> > > sb to be thawed */
> > >> > > + /* who froze superblock */
> > >> > > + char freeze_comm[16];
> > >> > Here should be TASK_COMM_LEN, shouldn't it?
> > >>
> > >> It will pull sched.h, dunno if we care about headers anymore.
> > > That's not ideal but IMHO better than having the value hardcoded here.
> > > That is pretty fragile - i.e. think what happens when someone decides to
> > > increase TASK_COMM_LEN...
> >
> > TASK_COMM_LEN is userspace ABI via at least prctl(PR_SET_NAME).
> > I can formally move it to include/uapi/linux/sched.h.
> > This allows to not drag sched.h into fs.h for one tiny define.
> OK, moving the definition would be preferable to me (and IMO also a
> cleanup).
Freezing and thawing are separate system calls, task which is supposed
to thaw filesystem/superblock can disappear due to crash or not thaw
due to a bug. At least record task name (we can't take task_struct
reference) to make support engineer's life easier.
Hopefully 16 bytes per superblock isn't much.
TASK_COMM_LEN definition (which is userspace ABI, see prctl(PR_SET_NAME)) is
moved to userspace exported header to not drag sched.h into every fs.h inclusion.
Signed-off-by: Alexey Dobriyan <[email protected]>
---
fs/block_dev.c | 12 ++++++++----
fs/ioctl.c | 22 ++++++++++++++++------
fs/super.c | 2 ++
include/linux/fs.h | 6 ++++++
include/linux/sched.h | 3 ---
include/uapi/linux/sched.h | 3 +++
6 files changed, 35 insertions(+), 13 deletions(-)
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -227,9 +227,11 @@ struct super_block *freeze_bdev(struct block_device *bdev)
sb = get_active_super(bdev);
if (!sb)
goto out;
- if (sb->s_op->freeze_super)
+ if (sb->s_op->freeze_super) {
error = sb->s_op->freeze_super(sb);
- else
+ if (error == 0)
+ get_task_comm(sb->s_writers.freeze_comm, current);
+ } else
error = freeze_super(sb);
if (error) {
deactivate_super(sb);
@@ -267,9 +269,11 @@ int thaw_bdev(struct block_device *bdev, struct super_block *sb)
if (!sb)
goto out;
- if (sb->s_op->thaw_super)
+ if (sb->s_op->thaw_super) {
error = sb->s_op->thaw_super(sb);
- else
+ if (error == 0)
+ memset(sb->s_writers.freeze_comm, 0, TASK_COMM_LEN);
+ } else
error = thaw_super(sb);
if (error) {
bdev->bd_fsfreeze_count++;
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -518,6 +518,7 @@ static int ioctl_fioasync(unsigned int fd, struct file *filp,
static int ioctl_fsfreeze(struct file *filp)
{
struct super_block *sb = file_inode(filp)->i_sb;
+ int rv;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
@@ -527,22 +528,31 @@ static int ioctl_fsfreeze(struct file *filp)
return -EOPNOTSUPP;
/* Freeze */
- if (sb->s_op->freeze_super)
- return sb->s_op->freeze_super(sb);
- return freeze_super(sb);
+ if (sb->s_op->freeze_super) {
+ rv = sb->s_op->freeze_super(sb);
+ if (rv == 0)
+ get_task_comm(sb->s_writers.freeze_comm, current);
+ } else
+ rv = freeze_super(sb);
+ return rv;
}
static int ioctl_fsthaw(struct file *filp)
{
struct super_block *sb = file_inode(filp)->i_sb;
+ int rv;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
/* Thaw */
- if (sb->s_op->thaw_super)
- return sb->s_op->thaw_super(sb);
- return thaw_super(sb);
+ if (sb->s_op->thaw_super) {
+ rv = sb->s_op->thaw_super(sb);
+ if (rv == 0)
+ memset(sb->s_writers.freeze_comm, 0, TASK_COMM_LEN);
+ } else
+ rv = thaw_super(sb);
+ return rv;
}
/*
--- a/fs/super.c
+++ b/fs/super.c
@@ -1351,6 +1351,7 @@ int freeze_super(struct super_block *sb)
* sees write activity when frozen is set to SB_FREEZE_COMPLETE.
*/
sb->s_writers.frozen = SB_FREEZE_COMPLETE;
+ get_task_comm(sb->s_writers.freeze_comm, current);
up_write(&sb->s_umount);
return 0;
}
@@ -1387,6 +1388,7 @@ int thaw_super(struct super_block *sb)
out:
sb->s_writers.frozen = SB_UNFROZEN;
+ memset(sb->s_writers.freeze_comm, 0, TASK_COMM_LEN);
smp_wmb();
wake_up(&sb->s_writers.wait_unfrozen);
deactivate_locked_super(sb);
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -33,6 +33,7 @@
#include <asm/byteorder.h>
#include <uapi/linux/fs.h>
+#include <uapi/linux/sched.h>
struct backing_dev_info;
struct export_operations;
@@ -1217,6 +1218,11 @@ struct sb_writers {
int frozen; /* Is sb frozen? */
wait_queue_head_t wait_unfrozen; /* queue for waiting for
sb to be thawed */
+ /*
+ * who froze superblock
+ * write-only field for traces in crashdump
+ */
+ char freeze_comm[TASK_COMM_LEN];
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map lock_map[SB_FREEZE_LEVELS];
#endif
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -303,9 +303,6 @@ extern char ___assert_task_state[1 - 2*!!(
#endif
-/* Task command name length */
-#define TASK_COMM_LEN 16
-
#include <linux/spinlock.h>
/*
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -49,4 +49,7 @@
*/
#define SCHED_FLAG_RESET_ON_FORK 0x01
+/* Task command name length */
+#define TASK_COMM_LEN 16
+
#endif /* _UAPI_LINUX_SCHED_H */
On Sat, Feb 28, 2015 at 05:25:57PM +0300, Alexey Dobriyan wrote:
> Freezing and thawing are separate system calls, task which is supposed
> to thaw filesystem/superblock can disappear due to crash or not thaw
> due to a bug. At least record task name (we can't take task_struct
> reference) to make support engineer's life easier.
>
> Hopefully 16 bytes per superblock isn't much.
>
> TASK_COMM_LEN definition (which is userspace ABI, see prctl(PR_SET_NAME)) is
> moved to userspace exported header to not drag sched.h into every fs.h inclusion.
>
> Signed-off-by: Alexey Dobriyan <[email protected]>
Freeze/thaw can be nested at the block level. That means the
sb->s_writers.freeze_comm can point at the wrong process. i.e.
Task A Task B
freeze_bdev
freeze_super
freeze_comm = A
freeze_bdev
.....
thaw_bdev
<device still frozen>
<crash>
At this point, the block device will never be unthawed, but
the debug field is now pointing to the wrong task. i.e. The debug
helper has not recorded the process that is actually causing the
problem, and leads us all off on a wild goose chase down the wrong
path.
IMO, debug code is only useful if it's reliable.....
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -303,9 +303,6 @@ extern char ___assert_task_state[1 - 2*!!(
>
> #endif
>
> -/* Task command name length */
> -#define TASK_COMM_LEN 16
> -
> #include <linux/spinlock.h>
>
> /*
> --- a/include/uapi/linux/sched.h
> +++ b/include/uapi/linux/sched.h
> @@ -49,4 +49,7 @@
> */
> #define SCHED_FLAG_RESET_ON_FORK 0x01
>
> +/* Task command name length */
> +#define TASK_COMM_LEN 16
> +
> #endif /* _UAPI_LINUX_SCHED_H */
That should be a separate patch, sent to the scheduler maintainers
for review. AFAICT, it isn't part of the user API - it's not defined
in the man page which just says "can be up to 16 bytes".
Cheers,
Dave.
--
Dave Chinner
[email protected]