Re: Problem with global_flush_tlb() on i386 in 2.6.22-rc4-mm2
* Anthony Liguori ([EMAIL PROTECTED]) wrote: > This is actually very conservative seeing as how disabling CR4.PGE > should be sufficient to flush global pages on modern processors. I > suspect you're getting preempted while it's running. > Sorry, I just realized that I rejected your preemption explanation without explaining why: 1 - In my "Text Section" lock code, which is the original place where I triggered the problem, I take a spinlock around these operations, which disables preemption. 2 - My sample module plays alone in its own data structures: there is only one thread accessing the data at a given time (because I do only one file open at a given time, which I control). Regards, Mathieu -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: Problem with global_flush_tlb() on i386 in 2.6.22-rc4-mm2
* Anthony Liguori ([EMAIL PROTECTED]) wrote:
> Mathieu Desnoyers wrote:
> >Hi,
> >
> >Trying to test my "Text Edit Lock" patches, I ran into a problem related
> >to global_flush_tlb() not doing its job at updating the page flags when,
> >it seems, the page has been recently accessed. Therefore, it can only be
> >reproduced by doing a couple of iterations.
> >
> >This is clearly the memory write I am trying to do in the page of
> >which I just changed the attributes to RWX.
> >
> >If I remove the variable read before I change the flags, it starts
> >working correctly (as far as I have tested...).
> >
> >If I use my own my_local_tlb_flush() function (not SMP aware) instead of
> >global_flush_tlb(), it works correctly.
> >
>
> What is your my_local_tlb_flush() and are you calling with preemption
> disabled?
>
The implementation was below in the email. Full preemption was enabled.
> >I also tried just calling clflush on the modified page just after the
> >global_flush_tlb(), and the problem was still there.
> >
> >I therefore suspect that
> >
> >include/asm-i386/tlbflush.h:
> >#define __native_flush_tlb_global() \
> >do {\
> >unsigned int tmpreg, cr4, cr4_orig; \
> >\
> >__asm__ __volatile__( \
> >"movl %%cr4, %2; # turn off PGE \n"\
> >"movl %2, %1;\n"\
> >"andl %3, %1;\n"\
> >"movl %1, %%cr4; \n"\
> >"movl %%cr3, %0; \n"\
> >"movl %0, %%cr3; # flush TLB\n"\
> >"movl %2, %%cr4; # turn PGE back on \n"\
> >: "=&r" (tmpreg), "=&r" (cr4), "=&r" (cr4_orig) \
> >: "i" (~X86_CR4_PGE)\
> >: "memory");\
> >} while (0)
> >
> >is not doing its job correctly. The problem does not seem to be caused
> >by PARAVIRT, because it is still buggy even if I disable the PARAVIRT
> >config option.
>
> This is actually very conservative seeing as how disabling CR4.PGE
> should be sufficient to flush global pages on modern processors. I
> suspect you're getting preempted while it's running.
>
Thanks for the advice, but please have a look at my follow-up on the
issue, where I spotted the problem more precisely. It also affects
ioremap, which also uses global_flush_tlb(). I guess this bug is worth
being fixed quickly, even if it is just by applying my workaround (which
is _really_ conservative).
Regards,
Mathieu
> Regards,
>
> Anthony Liguori
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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Re: Problem with global_flush_tlb() on i386 in 2.6.22-rc4-mm2
Mathieu Desnoyers wrote: Hi, Trying to test my "Text Edit Lock" patches, I ran into a problem related to global_flush_tlb() not doing its job at updating the page flags when, it seems, the page has been recently accessed. Therefore, it can only be reproduced by doing a couple of iterations. I run on a Pentium 4 with the following characteristics: processor : 0 vendor_id : GenuineIntel cpu family : 15 model : 4 model name : Intel(R) Pentium(R) 4 CPU 3.00GHz stepping: 1 cpu MHz : 3000.201 cache size : 1024 KB fdiv_bug: no hlt_bug : no f00f_bug: no coma_bug: no fpu : yes fpu_exception : yes cpuid level : 5 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx constant_tsc pebs bts sync_rdtsc pni monitor ds_cpl cid xtpr bogomips: 6007.49 clflush size: 64 config : CONFIG_X86_INVLPG=y (complete .config at the end) CONFIG_PARAVIRT=y/n (notice that pge and clflush features are present) The kernel is configured in UP (I first saw the problem in SMT, but switched to UP and it is still there). I provide a really crude hackish test module that shows the problematic behavior below. Whenever I run the module using global_flush_tlb(), I get the following OOPS: [ 1112.512389] Init Attr RX [ 1112.521691] Init Attr RX end [ 1113.702965] Loop 0 [ 1113.709171] Attr RWX 621545 [ 1113.717662] Attr RX 621545 [ 1113.725869] Attr RWX 432917 [ 1113.734295] Attr RX 432917 [ 1113.742460] Attr RWX 973425 [ 1113.750885] Attr RX 973425 [ 1113.759048] Attr RWX 453890 [ 1113.767490] Attr RX 453890 [ 1113.775653] Attr RWX 1035918 [ 1113.784341] Attr RX 1035918 [ 1113.792764] Attr RWX 1038276 [ 1113.801449] Attr RX 1038276 [ 1113.809902] Attr RWX 71394 [ 1113.818067] Attr RX 71394 [ 1113.825970] Attr RWX 88253 [ 1113.834134] Attr RX 88253 [ 1113.842039] Attr RWX 108029 [ 1113.850505] Attr RX 108029 [ 1113.858670] Attr RWX 767772 [ 1113.867095] Attr RX 767772 [ 1113.875259] Attr RWX 251394 [ 1113.883694] Attr RX 251394 [ 1113.891859] Attr RWX 817582 [ 1113.900376] Attr RX 817582 [ 1113.908540] Attr RWX 577819 [ 1113.916965] Attr RX 577819 [ 1113.925127] Attr RWX 56979 [ 1113.933293] Attr RX 56979 [ 1113.941195] Attr RWX 72953 [ 1113.949361] Attr RX 72953 [ 1113.957265] Attr RWX 94222 [ 1113.965445] BUG: unable to handle kernel paging request at virtual address c3a1700e [ 1113.988291] printing eip: [ 1113.996340] f885e0a6 [ 1114.002835] *pde = 038c6163 [ 1114.011145] *pte = 03a17163 [ 1114.019455] Oops: 0003 [#1] [ 1114.027766] PREEMPT [ 1114.034268] LTT NESTING LEVEL : 0 [ 1114.044402] Modules linked in: test_rodata ltt_statedump ltt_control sky2 skge rtc snd_hda_intel [ 1114.070679] CPU:0 [ 1114.070680] EIP:0060:[]Not tainted VLI [ 1114.070681] EFLAGS: 00010282 (2.6.22-rc4-mm2-testssmp #129) [ 1114.110395] EIP is at my_open+0xa6/0x124 [test_rodata] [ 1114.125711] eax: c3a0 ebx: 0001700e ecx: c39e4000 edx: [ 1114.145953] esi: 36f1700e edi: f885e000 ebp: c39e5ebc esp: c39e5ea0 [ 1114.166195] ds: 007b es: 007b fs: gs: 0033 ss: 0068 [ 1114.183583] Process cat (pid: 4112, ti=c39e4000 task=c38ac1b0 task.ti=c39e4000) [ 1114.204862] Stack: f885e223 0001700e f000 c31d3480 f885e000 c39e5ed8 [ 1114.229843]c01a3c2a c39d2540 c368d4a8 c39d2540 c368d4a8 c39e5ef8 c016f5d9 [ 1114.254830]c1c0eec0 c378ccfc c39e5eec c39d2540 8000 c39e5f1c c39e5f0c c016f76b [ 1114.279814] Call Trace: [ 1114.287620] [] proc_reg_open+0x42/0x68 [ 1114.301655] [] __dentry_open+0xe6/0x1e2 [ 1114.315944] [] nameidata_to_filp+0x35/0x3f [ 1114.331008] [] do_filp_open+0x3b/0x43 [ 1114.344777] [] do_sys_open+0x43/0x116 [ 1114.358545] [] sys_open+0x1c/0x1e [ 1114.371274] [] syscall_call+0x7/0xb [ 1114.384524] [] 0xe410 [ 1114.395178] === [ 1114.405823] INFO: lockdep is turned off. [ 1114.417504] Code: 60 df 7c c0 b9 63 01 00 00 ba 01 00 00 00 e8 3f 7d 8b c7 0f ae f0 89 f6 e8 5c 80 8b c7 0f ae f0 89 f6 a1 88 eb 85 f8 0f b6 55 f0 <88> 14 03 0f ae f0 89 f6 89 d8 03 05 88 eb 85 f8 05 00 00 00 40 [ 1114.474329] EIP: [] my_open+0xa6/0x124 [test_rodata] SS:ESP 0068:c39e5ea0 [ 1114.497187] BUG: sleeping function called from invalid context at kernel/rwsem.c:20 [ 1114.520025] in_atomic():0, irqs_disabled():1 [ 1114.532744] INFO: lockdep is turned off. [ 1114.544427] irq event stamp: 1894 [ 1114.554293] hardirqs last enabled at (1893): [] _spin_unlock_irq+0x22/0x4e [ 1114.577666] hardirqs last disabled at (1894): [] _spin_lock_irqsave+0x25/0x61 [ 1114.601556] softirqs last enabled at (1886): [] __do_softirq+0xe1/0x184 [ 1114.624149] softirqs last disabled at (1875): [] do_softirq+0x72/0x77 [ 1114.645969] [] dump_trace+0x1d5/0x204 [ 1114.659737] [] show_trace_log_lvl+0x1a/0x30 [ 1114.675060] [] show_trace+0x12/0x1
