linux-kernel - Re: [PATCH 1/2] drm/i915: set O_LARGEFILE in __create

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Message-ID: <zzkl4ozxohkkz6w6himarcecvsvboswwda3bypyj3nv7p56wia@2zn3cvfmzt6i>
Date: Thu, 21 Aug 2025 11:12:07 -0100
From: Andi Shyti <andi.shyti@...nel.org>
To: 陈涛涛 Taotao Chen <chentaotao@...iglobal.com>
Cc: "rodrigo.vivi@...el.com" <rodrigo.vivi@...el.com>, 
	"airlied@...il.com" <airlied@...il.com>, "brauner@...nel.org" <brauner@...nel.org>, 
	"intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>, "jani.nikula@...ux.intel.com" <jani.nikula@...ux.intel.com>, 
	"joonas.lahtinen@...ux.intel.com" <joonas.lahtinen@...ux.intel.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"lkp@...el.com" <lkp@...el.com>, "oe-lkp@...ts.linux.dev" <oe-lkp@...ts.linux.dev>, 
	"oliver.sang@...el.com" <oliver.sang@...el.com>, "simona@...ll.ch" <simona@...ll.ch>, 
	"tursulin@...ulin.net" <tursulin@...ulin.net>
Subject: Re: [PATCH 1/2] drm/i915: set O_LARGEFILE in __create_shmem()

Hi Taotao,

...

> >> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> >> index e3d188455f67..2b53aad915f5 100644
> >> --- a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> >> +++ b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> >> @@ -514,6 +514,11 @@ static int __create_shmem(struct drm_i915_private *i915,
> >>  	if (IS_ERR(filp))
> >>  		return PTR_ERR(filp);
> >>  
> >> +	/*
> >> +	 * Prevent -EFBIG by allowing large writes beyond MAX_NON_LFS on shmem
> >> +	 * objects by setting O_LARGEFILE.
> >> +	 */
> >> +	filp->f_flags |= O_LARGEFILE;
> >
> > I don't have anything against this, but is it really fixing the
> > issue? I thought that O_LARGEFILE is ignored in 64 bit machines,
> > while here the failure is happening in 64 bit machines.
> 
> As mentioned in the commit body, without O_LARGEFILE, file->f_op->write_iter
> calls generic_write_check_limits(), which enforces the 2GB (MAX_NON_LFS) limit
> and causes -EFBIG on large writes.
> 
> On 64-bit systems O_LARGEFILE is still set when opening files (e.g. via open()),
> so we also need to set it here for shmem objects created inside the kernel.
> 
> However, on older 32-bit systems, setting O_LARGEFILE unconditionally may be risky.
> Previously I did not check this, but to reduce the risk a safer approach is to wrap
> it in a check, for example:
> 
> +	if (force_o_largefile())
> +		filp->f_flags |= O_LARGEFILE;

Ack!

> > Besides, where do you see in the LKP logs the -EFBIG error
> > message?
> >
> 
> Due to the previous return order in shmem_pwrite(), this -EFBIG was being overwritten
> by -EIO on short writes. This issue will be fixed in PATCH 2/2.

Yes, correct :-)

Thanks,
Andi