In a process context kernel_read returns -EINTR, how to proceed?

In a process context kernel_read returns -EINTR, how to proceed?

[Lev Olshvang]

Hi All,

I use kernel_read to read  file in chunks of 4K size in a process context
On several files, like libc, libm,  I got -EINTR error.

Then I repeated the attempt limited number of times but still on every read attempt I got -EINTR

I do not understand who may interrupt such a small read, I suppose these libraries are already mapped in other processes so no real I/O should be done.

In a user space it is recommended to repeat syscall, what is the proper course of action in kernel.
As I stated, this code is not in a kernel thread or atomic context, it is in a process context so a tried  before next attempt yield() but to no success.

Waiting for your advises.
Thx,
Lev


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Re: In a process context kernel_read returns -EINTR, how to proceed?

[valdis.kletnieks]

On Thu, 20 Dec 2018 13:33:09 +0300, Lev Olshvang said:
> I use kernel_read to read  file in chunks of 4K size in a process context
> On several files, like libc, libm,  I got -EINTR error.

What are you trying to accomplish?  This is not a recommended way to do things.

> I do not understand who may interrupt such a small read, I suppose these
> libraries are already mapped in other processes so no real I/O should be done.

That should be a hint....

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Re: In a process context kernel_read returns -EINTR, how to proceed?

[Lev Olshvang]

Hi Valdis,

I need to read file  inside LSM hook and I can not do it in user space
I forgot o mention that same error occurried  both in 4.4 and 4.13 kernels
 What alternative you can recommend to read file in kernel and avoid -EINTR?
Is vfs_read() different from kernel_read() ?

ThanX
Lev

20.12.2018, 23:09, "valdis.kletnieks@vt.edu" <valdis.kletnieks@vt.edu>:
> On Thu, 20 Dec 2018 13:33:09 +0300, Lev Olshvang said:
>>  I use kernel_read to read file in chunks of 4K size in a process context
>>  On several files, like libc, libm, I got -EINTR error.
>
> What are you trying to accomplish? This is not a recommended way to do things.
>
>>  I do not understand who may interrupt such a small read, I suppose these
>>  libraries are already mapped in other processes so no real I/O should be done.
>
> That should be a hint....
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies@kernelnewbies.org
> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

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Re: In a process context kernel_read returns -EINTR, how to proceed?

[Greg KH]

On Fri, Dec 21, 2018 at 04:51:29PM +0300, Lev Olshvang wrote:
> Hi Valdis,
> 
> I need to read file  inside LSM hook and I can not do it in user space
> I forgot o mention that same error occurried  both in 4.4 and 4.13 kernels
>  What alternative you can recommend to read file in kernel and avoid -EINTR?
> Is vfs_read() different from kernel_read() ?

You should never try to read a file from within the kernel.

That way lies madness and lots and lots and lots of problems.

You really are on your own if you want to do that, you should step back
and reconsider exactly what you are trying to do and redesign your
system to not try to ever do this.

good luck!

greg k-h

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Re: In a process context kernel_read returns -EINTR, how to proceed?

[valdis.kletnieks]

On Fri, 21 Dec 2018 16:51:29 +0300, Lev Olshvang said:

> I need to read file  inside LSM hook and I can not do it in user space

Why? And which LSM hook are you trying to do this?

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Re: In a process context kernel_read returns -EINTR, how to proceed?

[Lev Olshvang]

I use  security_mmap_file hook.



21.12.2018, 19:15, "valdis.kletnieks@vt.edu" <valdis.kletnieks@vt.edu>:
> On Fri, 21 Dec 2018 16:51:29 +0300, Lev Olshvang said:
>
>>  I need to read file inside LSM hook and I can not do it in user space
>
> Why? And which LSM hook are you trying to do this?

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Re: In a process context kernel_read returns -EINTR, how to proceed?

[valdis.kletnieks]

On Sun, 23 Dec 2018 11:41:30 +0300, Lev Olshvang said:
> I use  security_mmap_file hook.

And what are you trying to accomplish in there?

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