* [REGRESSION] mm: filemap_map_pages NULL pointer dereference @ 2016-02-05 18:05 Jeremiah Mahler 2016-02-05 21:59 ` Andrew Morton 2016-02-05 22:19 ` Andrew Morton 0 siblings, 2 replies; 7+ messages in thread From: Jeremiah Mahler @ 2016-02-05 18:05 UTC (permalink / raw) To: linux-kernel; +Cc: Matthew Wilcox, Andrew Morton, Hugh Dickins, Mel Gorman all, On a Lenovo X1 Carbon running -next (20160201+, 20160203+) I have experienced several system hangs. I usually notice it first when my browser (Chrome) stops responding but then other programs will stop responding as well. The only fix is a reboot. It is sporadic but it will usually occur once a day. In the logs there will be a unable to handle kernel NULL pointer dereference message related to filemap_map_pages+0x10d/0x290 (below). ------------------------------------------------------------ ... [51985.993033] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 [51985.993087] IP: [<ffffffff8114a19d>] filemap_map_pages+0x10d/0x290 [51985.993123] PGD 2c772067 PUD 0 [51985.993144] Oops: 0000 [#1] SMP [51985.993166] Modules linked in: ctr ccm cpufreq_conservative cpufreq_stats cpufreq_userspace cpufreq_powersave binfmt_misc i915 arc4 iwldvm mac80211 x86_pkg_temp_thermal intel_powerclamp coretemp crct10dif_pclmul crc32_pclmul crc32c_intel iTCO_wdt ghash_clmulni_intel iTCO_vendor_support jitterentropy_rng sha256_generic hmac drbg snd_hda_codec_hdmi aesni_intel snd_hda_codec_realtek aes_x86_64 iwlwifi glue_helper snd_hda_codec_generic i2c_algo_bit lrw drm_kms_helper gf128mul ablk_helper cryptd snd_hda_intel drm psmouse snd_hda_codec cfg80211 pcspkr evdev serio_raw snd_hwdep i2c_i801 snd_hda_core sg snd_pcm mei_me lpc_ich mfd_core mei shpchp snd_timer i2c_core wmi thinkpad_acpi nvram snd battery tpm_tis soundcore ac tpm video button intel_smartconnect btusb btbcm btintel bluetooth rfkill loop ipv6 autofs4 [51985.993591] ext4 crc16 mbcache jbd2 sd_mod ahci libahci libata ehci_pci sdhci_pci scsi_mod xhci_pci sdhci xhci_hcd ehci_hcd mmc_core usbcore usb_common thermal [51985.993680] CPU: 2 PID: 22993 Comm: chrome Not tainted 4.5.0-rc2-next-20160203+ #11 [51985.993714] Hardware name: LENOVO 3443CTO/3443CTO, BIOS G6ET59WW (2.03 ) 09/11/2012 [51985.993760] task: ffff88004bb04dc0 ti: ffff88002a2f8000 task.ti: ffff88002a2f8000 [51985.993804] RIP: 0010:[<ffffffff8114a19d>] [<ffffffff8114a19d>] filemap_map_pages+0x10d/0x290 [51985.993845] RSP: 0000:ffff88002a2fbdf8 EFLAGS: 00010202 [51985.993874] RAX: 00000007fffffff8 RBX: 0000000000000001 RCX: 0000000000000003 [51985.993911] RDX: 0000000000000000 RSI: ffffea00005bdd1c RDI: ffffea00005bdd00 [51985.993948] RBP: ffff8800beff4220 R08: 000000000000007f R09: 0000000000000000 [51985.993985] R10: 0000000000000000 R11: ffff8800a39382b8 R12: ffff8801182b9440 [51985.994023] R13: ffff88002a2fbe90 R14: ffff8800be568d80 R15: 0000000000000008 [51985.994061] FS: 00007f3e20276a40(0000) GS:ffff88011e300000(0000) knlGS:0000000000000000 [51985.994103] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [51985.994134] CR2: 0000000000000008 CR3: 00000000be6eb000 CR4: 00000000001406e0 [51985.994172] Stack: [51985.994184] ffff8800beff4228 00007f3e0ae63000 0000000000000001 0000000000000000 [51985.994229] 0000000000000001 00007f3e0ae63000 ffff8800be568d80 0000000000000054 [51985.994273] ffff880000000318 ffff88003584c318 ffff8800840076c0 ffffffff8117b073 [51985.994318] Call Trace: [51985.994336] [<ffffffff8117b073>] ? handle_mm_fault+0x13b3/0x1790 [51985.994370] [<ffffffff810aa7f1>] ? up_write+0x21/0x30 [51985.994400] [<ffffffff81059052>] ? __do_page_fault+0x192/0x410 [51985.994434] [<ffffffff814ffcc8>] ? page_fault+0x28/0x30 [51985.994463] Code: 00 00 00 48 8b 54 24 10 49 3b 55 28 74 48 48 8b 44 24 18 83 e8 01 29 d0 49 8d 04 c7 49 39 c7 74 19 49 83 c7 08 48 83 44 24 10 01 <49> 83 3f 00 74 eb 4d 85 ff 0f 85 3b ff ff ff 48 8b 3c 24 48 8d [51985.994656] RIP [<ffffffff8114a19d>] filemap_map_pages+0x10d/0x290 [51985.994692] RSP <ffff88002a2fbdf8> [51985.994711] CR2: 0000000000000008 [51986.002154] ---[ end trace da60309b42c1da53 ]--- [52006.988971] INFO: rcu_sched self-detected stall on CPU [52006.988978] 3-...: (5249 ticks this GP) idle=765/140000000000001/0 softirq=931903/931903 fqs=5247 [52006.988980] (t=5250 jiffies g=821290 c=821289 q=1968) [52006.988982] Task dump for CPU 3: [52006.988985] CompositorTileW R running task 0 22999 1425 0x00000108 [52006.988988] ffffffff81851580 ffffffff81148a21 ffff88011e397540 ffffffff81851580 [52006.988991] 0000000000000000 ffff880117daa180 ffffffff810c5e19 0000000000983e0c [52006.988993] ffffffff810cfd7e 0000000000000092 0000000000000092 003b9aca00000000 [52006.988995] Call Trace: [52006.988996] <IRQ> [<ffffffff81148a21>] ? rcu_dump_cpu_stacks+0x71/0x8a [52006.989004] [<ffffffff810c5e19>] ? rcu_check_callbacks+0x6e9/0x790 [52006.989007] [<ffffffff810cfd7e>] ? timekeeping_update+0xee/0x150 [52006.989009] [<ffffffff810d8bd0>] ? tick_sched_handle.isra.14+0x50/0x50 [52006.989011] [<ffffffff810ca712>] ? update_process_times+0x32/0x60 [52006.989013] [<ffffffff810d8ba0>] ? tick_sched_handle.isra.14+0x20/0x50 [52006.989014] [<ffffffff810d8c08>] ? tick_sched_timer+0x38/0x70 [52006.989016] [<ffffffff810caf1c>] ? __hrtimer_run_queues+0xec/0x230 [52006.989017] [<ffffffff810cb5fa>] ? hrtimer_interrupt+0x9a/0x1a0 [52006.989020] [<ffffffff81500599>] ? smp_apic_timer_interrupt+0x39/0x50 [52006.989022] [<ffffffff814fea62>] ? apic_timer_interrupt+0x82/0x90 [52006.989023] <EOI> [<ffffffff812dfa05>] ? delay_tsc+0x25/0x50 [52006.989028] [<ffffffff810ac4d6>] ? do_raw_spin_lock+0x86/0x150 [52006.989031] [<ffffffff8117a175>] ? handle_mm_fault+0x4b5/0x1790 [52006.989033] [<ffffffff812e0be4>] ? call_rwsem_down_read_failed+0x14/0x30 [52006.989035] [<ffffffff81059052>] ? __do_page_fault+0x192/0x410 [52006.989037] [<ffffffff814ffcc8>] ? page_fault+0x28/0x30 ------------------------------------------------------------ Referring again to the RIP line from the trace. [51985.994656] RIP [<ffffffff8114a19d>] filemap_map_pages+0x10d/0x290 jeri@hudson:~/linux-next$ gdb vmlinux (gdb) list *0xffffffff8114a19d 0xffffffff8114a19d is in filemap_map_pages (include/linux/radix-tree.h:465). 460 unsigned size = radix_tree_chunk_size(iter) - 1; 461 462 while (size--) { 463 slot++; 464 iter->index++; 465 if (likely(*slot)) 466 return slot; 467 if (flags & RADIX_TREE_ITER_CONTIG) { 468 /* forbid switching to the next chunk */ 469 iter->next_index = 0; (gdb) Assuming I traced the addresses correctly, this indicates that the fault is triggered when the value in the slot pointer is accessed. Perhaps slot is being incremented beyond its valid range? -- - Jeremiah Mahler ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [REGRESSION] mm: filemap_map_pages NULL pointer dereference 2016-02-05 18:05 [REGRESSION] mm: filemap_map_pages NULL pointer dereference Jeremiah Mahler @ 2016-02-05 21:59 ` Andrew Morton 2016-02-05 22:19 ` Andrew Morton 1 sibling, 0 replies; 7+ messages in thread From: Andrew Morton @ 2016-02-05 21:59 UTC (permalink / raw) To: Jeremiah Mahler; +Cc: linux-kernel, Matthew Wilcox, Hugh Dickins, Mel Gorman On Fri, 5 Feb 2016 10:05:02 -0800 Jeremiah Mahler <jmmahler@gmail.com> wrote: > all, > > On a Lenovo X1 Carbon running -next (20160201+, 20160203+) I have > experienced several system hangs. I usually notice it first when > my browser (Chrome) stops responding but then other programs will stop > responding as well. The only fix is a reboot. It is sporadic but it > will usually occur once a day. > > In the logs there will be a > > unable to handle kernel NULL pointer dereference > > message related to filemap_map_pages+0x10d/0x290 (below). > > ------------------------------------------------------------ > ... > [51985.993033] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 > [51985.993087] IP: [<ffffffff8114a19d>] filemap_map_pages+0x10d/0x290 > [51985.993123] PGD 2c772067 PUD 0 > [51985.993144] Oops: 0000 [#1] SMP > [51985.993166] Modules linked in: ctr ccm cpufreq_conservative cpufreq_stats cpufreq_userspace cpufreq_powersave binfmt_misc i915 arc4 iwldvm mac80211 x86_pkg_temp_thermal intel_powerclamp coretemp crct10dif_pclmul crc32_pclmul crc32c_intel iTCO_wdt ghash_clmulni_intel iTCO_vendor_support jitterentropy_rng sha256_generic hmac drbg snd_hda_codec_hdmi aesni_intel snd_hda_codec_realtek aes_x86_64 iwlwifi glue_helper snd_hda_codec_generic i2c_algo_bit lrw drm_kms_helper gf128mul ablk_helper cryptd snd_hda_intel drm psmouse snd_hda_codec cfg80211 pcspkr evdev serio_raw snd_hwdep i2c_i801 snd_hda_core sg snd_pcm mei_me lpc_ich mfd_core mei shpchp snd_timer i2c_core wmi thinkpad_acpi nvram snd battery tpm_tis soundcore ac tpm video button intel_smartconnect btusb btbcm btintel bluetooth rfkill loop ipv6 autofs4 > [51985.993591] ext4 crc16 mbcache jbd2 sd_mod ahci libahci libata ehci_pci sdhci_pci scsi_mod xhci_pci sdhci xhci_hcd ehci_hcd mmc_core usbcore usb_common thermal > [51985.993680] CPU: 2 PID: 22993 Comm: chrome Not tainted 4.5.0-rc2-next-20160203+ #11 > [51985.993714] Hardware name: LENOVO 3443CTO/3443CTO, BIOS G6ET59WW (2.03 ) 09/11/2012 > [51985.993760] task: ffff88004bb04dc0 ti: ffff88002a2f8000 task.ti: ffff88002a2f8000 > [51985.993804] RIP: 0010:[<ffffffff8114a19d>] [<ffffffff8114a19d>] filemap_map_pages+0x10d/0x290 > [51985.993845] RSP: 0000:ffff88002a2fbdf8 EFLAGS: 00010202 > [51985.993874] RAX: 00000007fffffff8 RBX: 0000000000000001 RCX: 0000000000000003 > [51985.993911] RDX: 0000000000000000 RSI: ffffea00005bdd1c RDI: ffffea00005bdd00 > [51985.993948] RBP: ffff8800beff4220 R08: 000000000000007f R09: 0000000000000000 > [51985.993985] R10: 0000000000000000 R11: ffff8800a39382b8 R12: ffff8801182b9440 > [51985.994023] R13: ffff88002a2fbe90 R14: ffff8800be568d80 R15: 0000000000000008 > [51985.994061] FS: 00007f3e20276a40(0000) GS:ffff88011e300000(0000) knlGS:0000000000000000 > [51985.994103] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [51985.994134] CR2: 0000000000000008 CR3: 00000000be6eb000 CR4: 00000000001406e0 > [51985.994172] Stack: > [51985.994184] ffff8800beff4228 00007f3e0ae63000 0000000000000001 0000000000000000 > [51985.994229] 0000000000000001 00007f3e0ae63000 ffff8800be568d80 0000000000000054 > [51985.994273] ffff880000000318 ffff88003584c318 ffff8800840076c0 ffffffff8117b073 > [51985.994318] Call Trace: > [51985.994336] [<ffffffff8117b073>] ? handle_mm_fault+0x13b3/0x1790 > [51985.994370] [<ffffffff810aa7f1>] ? up_write+0x21/0x30 > [51985.994400] [<ffffffff81059052>] ? __do_page_fault+0x192/0x410 > [51985.994434] [<ffffffff814ffcc8>] ? page_fault+0x28/0x30 > [51985.994463] Code: 00 00 00 48 8b 54 24 10 49 3b 55 28 74 48 48 8b 44 24 18 83 e8 01 29 d0 49 8d 04 c7 49 39 c7 74 19 49 83 c7 08 48 83 44 24 10 01 <49> 83 3f 00 74 eb 4d 85 ff 0f 85 3b ff ff ff 48 8b 3c 24 48 8d > [51985.994656] RIP [<ffffffff8114a19d>] filemap_map_pages+0x10d/0x290 > [51985.994692] RSP <ffff88002a2fbdf8> > [51985.994711] CR2: 0000000000000008 > > ... > > Referring again to the RIP line from the trace. > > [51985.994656] RIP [<ffffffff8114a19d>] filemap_map_pages+0x10d/0x290 > > jeri@hudson:~/linux-next$ gdb vmlinux > (gdb) list *0xffffffff8114a19d > 0xffffffff8114a19d is in filemap_map_pages > (include/linux/radix-tree.h:465). > 460 unsigned size = radix_tree_chunk_size(iter) - 1; > 461 > 462 while (size--) { > 463 slot++; > 464 iter->index++; > 465 if (likely(*slot)) > 466 return slot; > 467 if (flags & RADIX_TREE_ITER_CONTIG) { > 468 /* forbid switching to the next chunk */ > 469 iter->next_index = 0; > (gdb) > > Assuming I traced the addresses correctly, this indicates that the > fault is triggered when the value in the slot pointer is accessed. > Perhaps slot is being incremented beyond its valid range? That's super helpful, thanks. The faulting address was 0x0000000000000008, so radix_tree_next_slot() was called with slot==NULL. And looking at it, I don't see how this code can work at all: : radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, vmf->pgoff) { : if (iter.index > vmf->max_pgoff) : break; : repeat: : page = radix_tree_deref_slot(slot); : if (unlikely(!page)) : goto next; : if (radix_tree_exception(page)) { : if (radix_tree_deref_retry(page)) { : slot = radix_tree_iter_retry(&iter); radix_tree_iter_retry() unconditionally returns NULL : continue; here we go and execute the third clause of the radix_tree_for_each_slot() `for' statement: slot = radix_tree_next_slot(slot, iter, 0)) with slot==NULL. This will dereference 0x8 every time. : } : goto next; : } ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [REGRESSION] mm: filemap_map_pages NULL pointer dereference 2016-02-05 18:05 [REGRESSION] mm: filemap_map_pages NULL pointer dereference Jeremiah Mahler 2016-02-05 21:59 ` Andrew Morton @ 2016-02-05 22:19 ` Andrew Morton 2016-02-06 18:18 ` Jeremiah Mahler 2016-02-07 15:50 ` Jeremiah Mahler 1 sibling, 2 replies; 7+ messages in thread From: Andrew Morton @ 2016-02-05 22:19 UTC (permalink / raw) To: Jeremiah Mahler Cc: linux-kernel, Matthew Wilcox, Hugh Dickins, Mel Gorman, Stephen Rothwell, Konstantin Khlebnikov On Fri, 5 Feb 2016 10:05:02 -0800 Jeremiah Mahler <jmmahler@gmail.com> wrote: > On a Lenovo X1 Carbon running -next (20160201+, 20160203+) I have > experienced several system hangs. I usually notice it first when > my browser (Chrome) stops responding but then other programs will stop > responding as well. The only fix is a reboot. It is sporadic but it > will usually occur once a day. > > In the logs there will be a > > unable to handle kernel NULL pointer dereference This should fix it up. From: Konstantin Khlebnikov <koct9i@gmail.com> Subject: radix-tree: fix oops after radix_tree_iter_retry Helper radix_tree_iter_retry() resets next_index to the current index. In following radix_tree_next_slot current chunk size becomes zero. This isn't checked and it tries to dereference null pointer in slot. Tagged iterator is fine because retry happens only at slot 0 where tag bitmask in iter->tags is filled with single bit. Fixes: 46437f9a554f ("radix-tree: fix race in gang lookup") Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com> Cc: Matthew Wilcox <willy@linux.intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Ohad Ben-Cohen <ohad@wizery.com> Cc: Jeremiah Mahler <jmmahler@gmail.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> --- include/linux/radix-tree.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff -puN include/linux/radix-tree.h~radix-tree-fix-oops-after-radix_tree_iter_retry include/linux/radix-tree.h --- a/include/linux/radix-tree.h~radix-tree-fix-oops-after-radix_tree_iter_retry +++ a/include/linux/radix-tree.h @@ -400,7 +400,7 @@ void **radix_tree_iter_retry(struct radi * @iter: pointer to radix tree iterator * Returns: current chunk size */ -static __always_inline unsigned +static __always_inline long radix_tree_chunk_size(struct radix_tree_iter *iter) { return iter->next_index - iter->index; @@ -434,9 +434,9 @@ radix_tree_next_slot(void **slot, struct return slot + offset + 1; } } else { - unsigned size = radix_tree_chunk_size(iter) - 1; + long size = radix_tree_chunk_size(iter); - while (size--) { + while (--size > 0) { slot++; iter->index++; if (likely(*slot)) _ ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [REGRESSION] mm: filemap_map_pages NULL pointer dereference 2016-02-05 22:19 ` Andrew Morton @ 2016-02-06 18:18 ` Jeremiah Mahler 2016-02-07 8:27 ` Konstantin Khlebnikov 2016-02-07 15:50 ` Jeremiah Mahler 1 sibling, 1 reply; 7+ messages in thread From: Jeremiah Mahler @ 2016-02-06 18:18 UTC (permalink / raw) To: Andrew Morton Cc: linux-kernel, Matthew Wilcox, Hugh Dickins, Mel Gorman, Stephen Rothwell, Konstantin Khlebnikov Andrew, On Fri, Feb 05, 2016 at 02:19:40PM -0800, Andrew Morton wrote: > On Fri, 5 Feb 2016 10:05:02 -0800 Jeremiah Mahler <jmmahler@gmail.com> wrote: > [...] > > unable to handle kernel NULL pointer dereference > > This should fix it up. > [...] > > include/linux/radix-tree.h | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff -puN include/linux/radix-tree.h~radix-tree-fix-oops-after-radix_tree_iter_retry include/linux/radix-tree.h > --- a/include/linux/radix-tree.h~radix-tree-fix-oops-after-radix_tree_iter_retry > +++ a/include/linux/radix-tree.h > @@ -400,7 +400,7 @@ void **radix_tree_iter_retry(struct radi > * @iter: pointer to radix tree iterator > * Returns: current chunk size > */ > -static __always_inline unsigned > +static __always_inline long > radix_tree_chunk_size(struct radix_tree_iter *iter) > { > return iter->next_index - iter->index; > @@ -434,9 +434,9 @@ radix_tree_next_slot(void **slot, struct > return slot + offset + 1; > } > } else { > - unsigned size = radix_tree_chunk_size(iter) - 1; > + long size = radix_tree_chunk_size(iter); > > - while (size--) { > + while (--size > 0) { > slot++; > iter->index++; > if (likely(*slot)) > _ > I have applied this patch to my kernel and so far the bug has not come back. Thanks for the quick fix. Although I don't quite understand how this fixes the slot==NULL problem. Unless I am missing something, it looks like the while loop will be executed the same number of times but the size variable will no longer go negative as it did before. -- - Jeremiah Mahler ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [REGRESSION] mm: filemap_map_pages NULL pointer dereference 2016-02-06 18:18 ` Jeremiah Mahler @ 2016-02-07 8:27 ` Konstantin Khlebnikov 2016-02-07 15:46 ` Jeremiah Mahler 0 siblings, 1 reply; 7+ messages in thread From: Konstantin Khlebnikov @ 2016-02-07 8:27 UTC (permalink / raw) To: Jeremiah Mahler, Andrew Morton, Linux Kernel Mailing List, Matthew Wilcox, Hugh Dickins, Mel Gorman, Stephen Rothwell, Konstantin Khlebnikov On Sat, Feb 6, 2016 at 9:18 PM, Jeremiah Mahler <jmmahler@gmail.com> wrote: > Andrew, > > On Fri, Feb 05, 2016 at 02:19:40PM -0800, Andrew Morton wrote: >> On Fri, 5 Feb 2016 10:05:02 -0800 Jeremiah Mahler <jmmahler@gmail.com> wrote: >> > [...] >> > unable to handle kernel NULL pointer dereference >> >> This should fix it up. >> > [...] >> >> include/linux/radix-tree.h | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff -puN include/linux/radix-tree.h~radix-tree-fix-oops-after-radix_tree_iter_retry include/linux/radix-tree.h >> --- a/include/linux/radix-tree.h~radix-tree-fix-oops-after-radix_tree_iter_retry >> +++ a/include/linux/radix-tree.h >> @@ -400,7 +400,7 @@ void **radix_tree_iter_retry(struct radi >> * @iter: pointer to radix tree iterator >> * Returns: current chunk size >> */ >> -static __always_inline unsigned >> +static __always_inline long >> radix_tree_chunk_size(struct radix_tree_iter *iter) >> { >> return iter->next_index - iter->index; >> @@ -434,9 +434,9 @@ radix_tree_next_slot(void **slot, struct >> return slot + offset + 1; >> } >> } else { >> - unsigned size = radix_tree_chunk_size(iter) - 1; >> + long size = radix_tree_chunk_size(iter); >> >> - while (size--) { >> + while (--size > 0) { >> slot++; >> iter->index++; >> if (likely(*slot)) >> _ >> > > I have applied this patch to my kernel and so far the bug has not > come back. Thanks for the quick fix. > > Although I don't quite understand how this fixes the slot==NULL problem. > Unless I am missing something, it looks like the while loop will be > executed the same number of times but the size variable will no > longer go negative as it did before. That's simple. Slot is dereferenced after checking remaining size. Old version checked only for != 0. After iter-retry size is zero and afrer "- 1" it overlaps into positive range. In new version it's signed and checked for > 0. > > -- > - Jeremiah Mahler ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [REGRESSION] mm: filemap_map_pages NULL pointer dereference 2016-02-07 8:27 ` Konstantin Khlebnikov @ 2016-02-07 15:46 ` Jeremiah Mahler 0 siblings, 0 replies; 7+ messages in thread From: Jeremiah Mahler @ 2016-02-07 15:46 UTC (permalink / raw) To: Konstantin Khlebnikov Cc: Andrew Morton, Linux Kernel Mailing List, Matthew Wilcox, Hugh Dickins, Mel Gorman, Stephen Rothwell Konstantin, On Sun, Feb 07, 2016 at 11:27:53AM +0300, Konstantin Khlebnikov wrote: > On Sat, Feb 6, 2016 at 9:18 PM, Jeremiah Mahler <jmmahler@gmail.com> wrote: [...] > >> -static __always_inline unsigned > >> +static __always_inline long > >> radix_tree_chunk_size(struct radix_tree_iter *iter) > >> { > >> return iter->next_index - iter->index; > >> @@ -434,9 +434,9 @@ radix_tree_next_slot(void **slot, struct > >> return slot + offset + 1; > >> } > >> } else { > >> - unsigned size = radix_tree_chunk_size(iter) - 1; > >> + long size = radix_tree_chunk_size(iter); > >> > >> - while (size--) { > >> + while (--size > 0) { > >> slot++; > >> iter->index++; > >> if (likely(*slot)) > >> _ > >> > > > > I have applied this patch to my kernel and so far the bug has not > > come back. Thanks for the quick fix. > > > > Although I don't quite understand how this fixes the slot==NULL problem. > > Unless I am missing something, it looks like the while loop will be > > executed the same number of times but the size variable will no > > longer go negative as it did before. > > That's simple. Slot is dereferenced after checking remaining size. > Old version checked only for != 0. After iter-retry size is zero and > afrer "- 1" it overlaps into positive range. In new version it's signed and > checked for > 0. > OK, I get it now. Thanks for the explanation. -- - Jeremiah Mahler ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [REGRESSION] mm: filemap_map_pages NULL pointer dereference 2016-02-05 22:19 ` Andrew Morton 2016-02-06 18:18 ` Jeremiah Mahler @ 2016-02-07 15:50 ` Jeremiah Mahler 1 sibling, 0 replies; 7+ messages in thread From: Jeremiah Mahler @ 2016-02-07 15:50 UTC (permalink / raw) To: Andrew Morton Cc: linux-kernel, Matthew Wilcox, Hugh Dickins, Mel Gorman, Stephen Rothwell, Konstantin Khlebnikov Konstantin, Andrew, On Fri, Feb 05, 2016 at 02:19:40PM -0800, Andrew Morton wrote: > On Fri, 5 Feb 2016 10:05:02 -0800 Jeremiah Mahler <jmmahler@gmail.com> wrote: > [...] > > This should fix it up. > > From: Konstantin Khlebnikov <koct9i@gmail.com> > Subject: radix-tree: fix oops after radix_tree_iter_retry > > Helper radix_tree_iter_retry() resets next_index to the current index. In > following radix_tree_next_slot current chunk size becomes zero. This > isn't checked and it tries to dereference null pointer in slot. > > Tagged iterator is fine because retry happens only at slot 0 where tag > bitmask in iter->tags is filled with single bit. > > Fixes: 46437f9a554f ("radix-tree: fix race in gang lookup") > Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com> > Cc: Matthew Wilcox <willy@linux.intel.com> > Cc: Hugh Dickins <hughd@google.com> > Cc: Ohad Ben-Cohen <ohad@wizery.com> > Cc: Jeremiah Mahler <jmmahler@gmail.com> > Cc: <stable@vger.kernel.org> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org> > --- > > include/linux/radix-tree.h | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff -puN include/linux/radix-tree.h~radix-tree-fix-oops-after-radix_tree_iter_retry include/linux/radix-tree.h > --- a/include/linux/radix-tree.h~radix-tree-fix-oops-after-radix_tree_iter_retry > +++ a/include/linux/radix-tree.h > @@ -400,7 +400,7 @@ void **radix_tree_iter_retry(struct radi > * @iter: pointer to radix tree iterator > * Returns: current chunk size > */ > -static __always_inline unsigned > +static __always_inline long > radix_tree_chunk_size(struct radix_tree_iter *iter) > { > return iter->next_index - iter->index; > @@ -434,9 +434,9 @@ radix_tree_next_slot(void **slot, struct > return slot + offset + 1; > } > } else { > - unsigned size = radix_tree_chunk_size(iter) - 1; > + long size = radix_tree_chunk_size(iter); > > - while (size--) { > + while (--size > 0) { > slot++; > iter->index++; > if (likely(*slot)) > _ > Fix is still working great after a couple days. Tested-by: Jeremiah Mahler <jmmahler@gmail.com> -- - Jeremiah Mahler ^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2016-02-07 15:50 UTC | newest] Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2016-02-05 18:05 [REGRESSION] mm: filemap_map_pages NULL pointer dereference Jeremiah Mahler 2016-02-05 21:59 ` Andrew Morton 2016-02-05 22:19 ` Andrew Morton 2016-02-06 18:18 ` Jeremiah Mahler 2016-02-07 8:27 ` Konstantin Khlebnikov 2016-02-07 15:46 ` Jeremiah Mahler 2016-02-07 15:50 ` Jeremiah Mahler
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