This looks a bit like a hack and it doesn't look right, conceptually. If the call fails, it should restore things as if nothing has ever happened and overwriting old_mapping is not going to do the trick. I think the right way to fix it would be to separately store the original mapping for filp->f_mapping and inode->i_mapping and restore it from their respective temporary variables if drm_open_helper or drm_setup fail. Attached is a quick patch to show you what I have in mind, can you please test it and if it solves your problem, I'll send it to Dave. By the way, what specific course of action reproduces the problem? It requires drm_open to fail, but is there anything else that you do? thanks, Ilija On Tue, Mar 26, 2013 at 3:56 PM, Michal Hocko <mhocko@xxxxxxx> wrote: > Hi, > the patch bellow fixes a nullptr dereference reported with OpenSUSE12.3. > I am not familiar with the area so I have no idea whether this is the > right way to go but after applying this patch the problem is not > reproducible anymore > If the patch is correct then please mark it for stable (3.7+). > > Thanks! > --- > From a786a701bd6c277329e2b788fea9a69b1c3ced2e Mon Sep 17 00:00:00 2001 > From: Michal Hocko <mhocko@xxxxxxx> > Date: Tue, 26 Mar 2013 19:04:40 +0100 > Subject: [PATCH] drm: fix i_mapping and f_mapping initialization in drm_open > in error path > > Starting with fdb40a08 (drm: set dev_mapping before calling > drm_open_helper) inode and file mappings are set to old_mapping in the > error path. old_mapping can be NULL, however, which is handled by > initializing dev_mapping to default inode->i_data. old_mapping is left > intact though so the both inode's and filep's mapping will still point > to NULL which is unexpected and can it results in crashes later one. > > Marco Munderloh has reported such crashes: > BUG: unable to handle kernel NULL pointer dereference at 0000000000000058 > IP: [<ffffffff81190be4>] drop_pagecache_sb+0x74/0xe0 > PGD 252bc1067 PUD 253d11067 PMD 0 > Oops: 0000 [#1] SMP > Modules linked in: fuse af_packet xt_tcpudp xt_pkttype xt_LOG xt_limit bnep bluetooth ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 > ip6table_raw ipt_REJECT iptable_raw xt_CT iptable_filter ip6table_mangle nf_conntrack_netbios_ns nf_conntrack_broadcast nf_conntrack_ipv4 nf_defrag_ipv4 ip_tables xt_conntrack nf_conntrack ip6table_filter ip6_tables x_tables cpufreq_conservative cpufreq_userspace cpufreq_powersave acpi_cpufreq snd_hda_codec_hdmi mperf coretemp snd_hda_codec_realtek snd_hda_intel snd_hda_codec snd_hwdep kvm_intel snd_pcm arc4 snd_seq snd_timer snd_seq_device kvm iwldvm mac80211 snd uvcvideo crc32c_intel videobuf2_core videodev ghash_clmulni_intel aesni_intel ablk_helper cryptd lrw videobuf2_vmalloc aes_x86_64 iTCO_wdt xts tpm_infineon mei r8169 videobuf2_memops iTCO_vendor_support sr_mod lpc_ich iwlwifi gf128mul sony_laptop rts_pstor(C) cdrom i2c_i801 tpm_tis tpm tpm_bios battery mfd_core soundcore snd_page_alloc cfg80211 rfkill ac sg microcode pcspkr autofs4 xhci_hcd ehci_hcd usbcore usb_common radeon i915 video ttm drm_kms_helper drm i2c_algo_bit thermal button processor thermal_sys scsi_dh_emc scsi_dh_rdac scsi_dh_hp_sw scsi_dh_alua > scsi_dh > CPU 0 > Pid: 1452, comm: bash Tainted: G C 3.7.10-1.1-default > ation VPCSA4W9E/VAIO > RIP: 0010:[<ffffffff81190be4>] [<ffffffff81190be4>] drop_pagecache_sb+0x74/0xe0 > RSP: 0018:ffff880252bc9e18 EFLAGS: 00010246 > RAX: 0000000000000000 RBX: ffff88024ecb7db0 RCX: 0000000000000002 > RDX: 0000000000000007 RSI: ffff88024f63a670 RDI: ffff88024ecb7e38 > RBP: ffff88024ecb7e38 R08: dead000000200200 R09: 0000000000000000 > R10: 0000000000000001 R11: 0000000000000210 R12: ffff880254d588a0 > R13: ffff88024fcb25e8 R14: ffffffff81190b70 R15: ffffffffffffffea > FS: 00007fad2b9ed700(0000) GS:ffff88025fa00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000000058 CR3: 0000000252ad2000 CR4: 00000000000407f0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 > Process bash (pid: 1452, threadinfo ffff880252bc8000, task ffff880253d321c0) > Stack: > 0000000000000001 ffff880254d58800 ffff880254e94800 ffff880254d58868 > 0000000000000000 ffffffff8116a499 0000000000000000 0000000000000001 > ffffffff81a228a0 ffff880252bc9f50 0000000000000002 ffffffff81190cce > Call Trace: > [<ffffffff8116a499>] iterate_supers+0xd9/0xe0 > [<ffffffff81190cce>] drop_caches_sysctl_handler+0x7e/0x90 > [<ffffffff811d0e26>] proc_sys_call_handler.isra.10+0xc6/0xe0 > [<ffffffff81166fd7>] vfs_write+0xa7/0x180 > [<ffffffff81167321>] sys_write+0x51/0xa0 > [<ffffffff8154f2ed>] system_call_fastpath+0x1a/0x1f > [<00007fad2ae959c0>] 0x7fad2ae959bf > Code: 01 00 00 49 39 c4 48 8d 98 00 ff ff ff 74 68 48 8d ab 88 00 00 00 48 89 ef e8 49 69 3b 00 f6 83 a0 00 00 00 38 75 d0 48 8b 43 30 <48> 83 78 58 00 74 c5 48 89 df e8 dd ef fe ff 66 83 45 00 01 66 > RIP [<ffffffff81190be4>] drop_pagecache_sb+0x74/0xe0 > RSP <ffff880252bc9e18> > CR2: 0000000000000058 > > when dropping caches when inode with NULL i_mapping is encountered. Or a > different one when umounting devtmpfs: > BUG: unable to handle kernel NULL pointer dereference at 0000000000000068 > IP: [<ffffffff81122001>] shmem_evict_inode+0x11/0x130 > PGD 0 > Oops: 0000 [#1] SMP > Modules linked in: xt_tcpudp xt_pkttype xt_LOG xt_limit af_packet ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_raw ipt_REJECT iptable_raw xt_CT iptable_filter ip6table_mangle nf_conntrack_netbios_ns nf_conntrack_broadcast nf_conntrack_ipv4 nf_defrag_ipv4 ip_tables xt_conntrack nf_conntrack bnep bluetooth ip6table_filter ip6_tables cpufreq_conservative x_tables cpufreq_userspace cpufreq_powersave snd_hda_codec_hdmi snd_hda_codec_realtek acpi_cpufreq snd_hda_intel mperf snd_hda_codec coretemp snd_hwdep kvm_intel snd_pcm kvm arc4 snd_seq iwldvm mac80211 crc32c_intel ghash_clmulni_intel snd_timer aesni_intel snd_seq_device iTCO_wdt uvcvideo videobuf2_core iwlwifi videodev sony_laptop videobuf2_vmalloc videobuf2_memops ablk_helper iTCO_vendor_support cryptd cfg80211 tpm_infineon r8169 sr_mod cdrom mei snd lpc_ich battery lrw aes_x86_64 xts rfkill i2c_i801 pcspkr mfd_core tpm_tis ac gf128mul tpm tpm_bios soundcore snd_page_alloc sg microcode autofs4 xhci_hcd ehci_hcd radeon(-) i915 ttm drm_kms_helper usbcore usb_common drm thermal i2c_algo_bit video button processor thermal_sys scsi_dh_emc scsi_dh_rdac scsi_dh_hp_sw scsi_dh_alua scsi_dh > CPU 1 <4>[ 44.175256] Pid: 29, comm: kdevtmpfs Tainted: G W 3.7.10-1-default-patched #4 Sony Corpora > tion VPCSA4W9E/VAIO > RIP: 0010:[<ffffffff81122001>] [<ffffffff81122001>] shmem_evict_inode+0x11/0x130 > RSP: 0018:ffff880254ed3d18 EFLAGS: 00010296 > RAX: 0000000000000000 RBX: ffff88024fb185e8 RCX: 0000000000000034 > RDX: 0000000000002433 RSI: 0000000000000c11 RDI: ffff88024fb185e8 > RBP: ffff88024fb186e8 R08: 1038000000000000 R09: 024fb186881c0000 > R10: fd924f0d6445a207 R11: 0000000000000000 R12: ffffffff8161b640 > R13: ffff88024fb185e8 R14: 0000000000000000 R15: 0000000000000000 > FS: 0000000000000000(0000) GS:ffff88025fa40000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000000068 CR3: 0000000001a0c000 CR4: 00000000000407e0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 > Process kdevtmpfs (pid: 29, threadinfo ffff880254ed2000, task ffff880254ed0080) > Stack: > ffff88024fb185e8 ffff88024fb185e8 ffff88024fb186e8 ffffffff8161b640 > 0000000000000000 ffffffff8117f5f3 ffff88024e453a80 ffff88024fb185e8 > 0000000000000000 ffffffff8117b778 0000000000000000 ffff88024e453a80 > Call Trace: > [<ffffffff8117f5f3>] evict+0xa3/0x190 > [<ffffffff8117b778>] d_delete+0x148/0x180 > [<ffffffff81171d77>] vfs_unlink+0xf7/0x110 > [<ffffffff81386ab2>] handle_remove+0x202/0x250 > [<ffffffff81386de5>] devtmpfsd+0xd5/0x130 > [<ffffffff81066273>] kthread+0xb3/0xc0 > [<ffffffff81549c3c>] ret_from_fork+0x7c/0xb0 > Code: 7b 30 b9 01 00 00 00 31 d2 4c 89 f6 e8 69 e3 00 00 e9 23 ff ff ff 0f 1f 40 00 41 55 49 89 fd 41 54 55 53 48 83 ec 08 48 8b 47 30 <48> 81 78 68 00 b7 61 81 74 75 48 8b 7f a8 4d 8d 65 90 e8 b8 1f > RIP [<ffffffff81122001>] shmem_evict_inode+0x11/0x130 > RSP <ffff880254ed3d18> > CR2: 0000000000000068 > > This patch fixes that by initializating old_mapping to the inode->i_data > same as dev_mapping. > > Reported-and-tested-by: Marco Munderloh <munderl@xxxxxxxxxxxxxxxxxxx> > Signed-off-by: Michal Hocko <mhocko@xxxxxxx> > --- > drivers/gpu/drm/drm_fops.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c > index 133b413..62a5435 100644 > --- a/drivers/gpu/drm/drm_fops.c > +++ b/drivers/gpu/drm/drm_fops.c > @@ -139,7 +139,7 @@ int drm_open(struct inode *inode, struct file *filp) > mutex_lock(&dev->struct_mutex); > old_mapping = dev->dev_mapping; > if (old_mapping == NULL) > - dev->dev_mapping = &inode->i_data; > + dev->dev_mapping = old_mapping = &inode->i_data; > /* ihold ensures nobody can remove inode with our i_data */ > ihold(container_of(dev->dev_mapping, struct inode, i_data)); > inode->i_mapping = dev->dev_mapping; > -- > 1.7.10.4 > > -- > Michal Hocko > SUSE Labs
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