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SubjectRe: [linux-next] mm/i915: i915_gemfs_init() NULL dereference
On (07/21/19 23:29), Sergey Senozhatsky wrote:
>
> BUG: kernel NULL pointer dereference, address: 0000000000000000
> #PF: supervisor instruction fetch in kernel mode
> #PF: error_code(0x0010) - not-present page
> PGD 0 P4D 0
> Oops: 0010 [#1] PREEMPT SMP PTI
> 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
> ? 0xffffffffc0522000
> do_one_initcall+0x37/0x13f
> ? kmem_cache_alloc+0x11a/0x150
> do_init_module+0x51/0x200
> __se_sys_init_module+0xef/0x100
> do_syscall_64+0x49/0x250
> entry_SYSCALL_64_after_hwframe+0x44/0xa9


So "the new mount API" conversion probably looks like something below.
But I'm not 100% sure.

---
drivers/gpu/drm/i915/gem/i915_gemfs.c | 32 +++++++++++++++++++++------
1 file changed, 25 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..2e365b26f8ee 100644
--- a/drivers/gpu/drm/i915/gem/i915_gemfs.c
+++ b/drivers/gpu/drm/i915/gem/i915_gemfs.c
@@ -7,12 +7,14 @@
#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;
struct file_system_type *type;
struct vfsmount *gemfs;

@@ -36,19 +38,35 @@ 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;

- 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))
+ goto err;
+
+ if (!fc->ops->parse_monolithic)
+ goto err;
+
+ err = fc->ops->parse_monolithic(fc, options);
+ if (err)
+ goto err;
+
+ if (!fc->ops->reconfigure)
+ goto err;
+
+ err = fc->ops->reconfigure(fc);
+ if (err)
+ goto err;
}

i915->mm.gemfs = gemfs;
-
return 0;
+
+err:
+ pr_err("i915 gemfs init() failed\n");
+ put_fs_context(fc);
+ kern_unmount(gemfs);
+ return -EINVAL;
}

void i915_gemfs_fini(struct drm_i915_private *i915)
--
2.22.0
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