Hi

Am 18.03.22 um 01:50 schrieb Chuansheng Liu:

Easily hit the below list corruption:

list_add corruption. prev->next should be next (ffffffffc0ceb090), but was ffffec604507edc8. (prev=ffffec604507edc8). WARNING: CPU: 65 PID: 3959 at lib/list_debug.c:26 __list_add_valid+0x53/0x80 CPU: 65 PID: 3959 Comm: fbdev Tainted: G U RIP: 0010:__list_add_valid+0x53/0x80 Call Trace:

<TASK> fb_deferred_io_mkwrite+0xea/0x150 do_page_mkwrite+0x57/0xc0 do_wp_page+0x278/0x2f0 __handle_mm_fault+0xdc2/0x1590 handle_mm_fault+0xdd/0x2c0 do_user_addr_fault+0x1d3/0x650 exc_page_fault+0x77/0x180 ? asm_exc_page_fault+0x8/0x30 asm_exc_page_fault+0x1e/0x30 RIP: 0033:0x7fd98fc8fad1 ==

Figure out the race happens when one process is adding &page->lru into the pagelist tail in fb_deferred_io_mkwrite(), another process is re-initializing the same &page->lru in fb_deferred_io_fault(), which is not protected by the lock.

This fix is to init all the page lists one time during initialization, it not only fixes the list corruption, but also avoids INIT_LIST_HEAD() redundantly.

V2: change "int i" to "unsigned int i" (Geert Uytterhoeven)

Thanks a lot. I added to patch to drm-misc-next.

Best regards Thomas

Fixes: 105a940416fc ("fbdev/defio: Early-out if page is already enlisted") Cc: Thomas Zimmermann tzimmermann@suse.de Cc: Geert Uytterhoeven geert@linux-m68k.org Reviewed-by: Javier Martinez Canillas javierm@redhat.com Reviewed-by: Thomas Zimmermann tzimmermann@suse.de Signed-off-by: Chuansheng Liu chuansheng.liu@intel.com

---

drivers/video/fbdev/core/fb_defio.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c index 98b0f23bf5e2..a1da54016c88 100644 --- a/drivers/video/fbdev/core/fb_defio.c +++ b/drivers/video/fbdev/core/fb_defio.c @@ -59,7 +59,6 @@ static vm_fault_t fb_deferred_io_fault(struct vm_fault *vmf) printk(KERN_ERR "no mapping available\n");

BUG_ON(!page->mapping);

• INIT_LIST_HEAD(&page->lru); page->index = vmf->pgoff;

  vmf->page = page;

@@ -220,6 +219,8 @@ static void fb_deferred_io_work(struct work_struct *work) void fb_deferred_io_init(struct fb_info *info) { struct fb_deferred_io *fbdefio = info->fbdefio;

• struct page *page;

• unsigned int i;

  BUG_ON(!fbdefio); mutex_init(&fbdefio->lock);

@@ -227,6 +228,12 @@ void fb_deferred_io_init(struct fb_info *info) INIT_LIST_HEAD(&fbdefio->pagelist); if (fbdefio->delay == 0) /* set a default of 1 s */ fbdefio->delay = HZ;

• /* initialize all the page lists one time */
• for (i = 0; i < info->fix.smem_len; i += PAGE_SIZE) {

• page = fb_deferred_io_page(info, i);
  

• INIT_LIST_HEAD(&page->lru);
  

• } } EXPORT_SYMBOL_GPL(fb_deferred_io_init);