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SubjectRe: [PATCH 1/2] i915: convert to new mount API
Date
Quoting Sergey Senozhatsky (2019-08-02 13:39:55)
> tmpfs does not set ->remount_fs() anymore and its users need
> to be converted to new mount API.
>
> BUG: kernel NULL pointer dereference, address: 0000000000000000
> PF: supervisor instruction fetch in kernel mode
> PF: error_code(0x0010) - not-present page
> RIP: 0010:0x0
> Code: Bad RIP value.
> Call Trace:
> i915_gemfs_init+0x6e/0xa0 [i915]
> i915_gem_init_early+0x76/0x90 [i915]
> i915_driver_probe+0x30a/0x1640 [i915]
> ? kernfs_activate+0x5a/0x80
> ? kernfs_add_one+0xdd/0x130
> pci_device_probe+0x9e/0x110
> really_probe+0xce/0x230
> driver_probe_device+0x4b/0xc0
> device_driver_attach+0x4e/0x60
> __driver_attach+0x47/0xb0
> ? device_driver_attach+0x60/0x60
> bus_for_each_dev+0x61/0x90
> bus_add_driver+0x167/0x1b0
> driver_register+0x67/0xaa
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> ---
> drivers/gpu/drm/i915/gem/i915_gemfs.c | 28 ++++++++++++++++++++-------
> 1 file changed, 21 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gemfs.c b/drivers/gpu/drm/i915/gem/i915_gemfs.c
> index 099f3397aada..cf05ba72df9d 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gemfs.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gemfs.c
> @@ -7,14 +7,17 @@
> #include <linux/fs.h>
> #include <linux/mount.h>
> #include <linux/pagemap.h>
> +#include <linux/fs_context.h>
>
> #include "i915_drv.h"
> #include "i915_gemfs.h"
>
> int i915_gemfs_init(struct drm_i915_private *i915)
> {
> + struct fs_context *fc = NULL;
> struct file_system_type *type;
> struct vfsmount *gemfs;
> + bool ok = true;

Start with ok = false, we only need to set to true if we succeed in
reconfiguring.

> type = get_fs_type("tmpfs");
> if (!type)
> @@ -36,18 +39,29 @@ int i915_gemfs_init(struct drm_i915_private *i915)
> struct super_block *sb = gemfs->mnt_sb;
> /* FIXME: Disabled until we get W/A for read BW issue. */
> char options[] = "huge=never";
> - int flags = 0;
> - int err;

Hmm, we could avoid this if we used vfs_kernel_mount() directly rather
than the kern_mount wrapper, as then we pass options through to
parse_monotithic_mount_data(). Or am I barking up the wrong tree?

>
> - err = sb->s_op->remount_fs(sb, &flags, options);
> - if (err) {
> - kern_unmount(gemfs);
> - return err;
> + fc = fs_context_for_reconfigure(sb->s_root, 0, 0);
> + if (IS_ERR(fc)) {
> + ok = false;
> + goto out;
> }
> +
> + if (!fc->ops->parse_monolithic ||
> + fc->ops->parse_monolithic(fc, options)) {

checkpatch.pl will complain that this should line up with the '('

> + ok = false;
> + goto out;
> + }
> +
> + if (!fc->ops->reconfigure || fc->ops->reconfigure(fc))
> + ok = false;
> }
>
> +out:
> + if (!ok)
> + pr_err("i915 gemfs reconfiguration failed\n");

Let's make it a bit more user friendly,

dev_err(i915->drm.dev,
"Unable to reconfigure internal shmemfs for preferred"
" allocation strategy; continuing, but performance may suffer.\n");

Assuming that we can't just use vfs_kern_mount() instead, with the nits
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
-Chris

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