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Fix race conditions in validate_mem via atomics

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When atomics are not available, the address cache is disabled.

Fixes data race found by TSAN:

WARNING: ThreadSanitizer: data race (pid=17824)
  Read of size 8 at 0x7f4dac484140 by thread T3:
    #0 validate_mem ../../src/x86_64/Ginit.c:201 (libunwind.so.
8+0x00000001f836)
    #1 access_mem ../../src/x86_64/Ginit.c:242 (libunwind.so.8+0x00000001fe06)
    #2 dwarf_get ../../include/tdep-x86_64/libunwind_i.h:168 (libunwind.so.
8+0x0000000221cf)
    #3 _ULx86_64_access_reg ../../src/x86_64/Gregs.c:130 (libunwind.so.
8+0x000000022e99)
    #4 _ULx86_64_get_reg ../../src/mi/Gget_reg.c:40 (libunwind.so.
8+0x00000001e5bc)
    #5 apply_reg_state ../../src/dwarf/Gparser.c:796 (libunwind.so.
8+0x000000038209)
    #6 _ULx86_64_dwarf_step ../../src/dwarf/Gparser.c:961 (libunwind.so.
8+0x000000039dbc)
    #7 _ULx86_64_step ../../src/x86_64/Gstep.c:71 (libunwind.so.
8+0x00000002481f)
    #8 trace_init_addr ../../src/x86_64/Gtrace.c:248 (libunwind.so.
8+0x000000026f0e)
    #9 trace_lookup ../../src/x86_64/Gtrace.c:330 (libunwind.so.
8+0x000000027429)
    #10 _ULx86_64_tdep_trace ../../src/x86_64/Gtrace.c:447 (libunwind.so.
8+0x00000002789a)
    #11 unw_backtrace ../../src/mi/backtrace.c:69 (libunwind.so.
8+0x00000001cb07)

  Previous write of size 8 at 0x7f4dac484140 by thread T2:
    #0 validate_mem ../../src/x86_64/Ginit.c:220 (libunwind.so.
8+0x00000001fc54)
    #1 access_mem ../../src/x86_64/Ginit.c:242 (libunwind.so.8+0x00000001fe06)
    #2 dwarf_get ../../include/tdep-x86_64/libunwind_i.h:168 (libunwind.so.
8+0x0000000221cf)
    #3 _ULx86_64_access_reg ../../src/x86_64/Gregs.c:130 (libunwind.so.
8+0x000000022e99)
    #4 _ULx86_64_get_reg ../../src/mi/Gget_reg.c:40 (libunwind.so.
8+0x00000001e5bc)
    #5 apply_reg_state ../../src/dwarf/Gparser.c:796 (libunwind.so.
8+0x000000038209)
    #6 _ULx86_64_dwarf_step ../../src/dwarf/Gparser.c:961 (libunwind.so.
8+0x000000039dbc)
    #7 _ULx86_64_step ../../src/x86_64/Gstep.c:71 (libunwind.so.
8+0x00000002481f)
    #8 trace_init_addr ../../src/x86_64/Gtrace.c:248 (libunwind.so.
8+0x000000026f0e)
    #9 trace_lookup ../../src/x86_64/Gtrace.c:330 (libunwind.so.
8+0x000000027429)
    #10 _ULx86_64_tdep_trace ../../src/x86_64/Gtrace.c:447 (libunwind.so.
8+0x00000002789a)
    #11 unw_backtrace ../../src/mi/backtrace.c:69 (libunwind.so.
8+0x00000001cb07)

  Location is global 'last_good_addr' of size 32 at 0x7f4dac484140
(libunwind.so.8+0x000000273140)
This commit is contained in:
Milian Wolff 2018-04-24 15:41:21 +02:00 committed by Milian Wolff
parent 3f689c9ee1
commit 3d473e183d
1 changed files with 50 additions and 21 deletions
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71
src/x86_64/Ginit.c
View file

@ -174,14 +174,56 @@ tdep_init_mem_validate (void)
}
/* Cache of already validated addresses */
#if HAVE_ATOMIC_OPS_H
#define NLGA 4
static unw_word_t last_good_addr[NLGA];
static int lga_victim;
static AO_T last_good_addr[NLGA];
static AO_T lga_victim;
static int
is_cached_valid_mem(unw_word_t addr)
{
int i;
for (i = 0; i < NLGA; i++)
{
if (addr == AO_load(&last_good_addr[i]))
return 1;
}
return 0;
}
static void
cache_valid_mem(unw_word_t addr)
{
int i, victim;
victim = AO_load(&lga_victim);
for (i = 0; i < NLGA; i++) {
if (AO_compare_and_swap(&last_good_addr[victim], 0, addr)) {
return;
}
victim = (victim + 1) % NLGA;
}
/* All slots full. Evict the victim. */
AO_store(&last_good_addr[victim], addr);
victim = (victim + 1) % NLGA;
AO_store(&lga_victim, victim);
}
#else
static int
is_cached_valid_mem(unw_word_t addr UNUSED)
{
return 0;
}
static void
cache_valid_mem(unw_word_t addr UNUSED)
{
}
#endif
static int
validate_mem (unw_word_t addr)
{
int i, victim;
size_t len;
if (PAGE_START(addr + sizeof (unw_word_t) - 1) == PAGE_START(addr))
@ -194,28 +236,13 @@ validate_mem (unw_word_t addr)
if (addr == 0)
return -1;
for (i = 0; i < NLGA; i++)
{
if (last_good_addr[i] && (addr == last_good_addr[i]))
return 0;
}
if (is_cached_valid_mem(addr))
return 0;
if (mem_validate_func ((void *) addr, len) == -1)
return -1;
victim = lga_victim;
for (i = 0; i < NLGA; i++) {
if (!last_good_addr[victim]) {
last_good_addr[victim++] = addr;
return 0;
}
victim = (victim + 1) % NLGA;
}
/* All slots full. Evict the victim. */
last_good_addr[victim] = addr;
victim = (victim + 1) % NLGA;
lga_victim = victim;
cache_valid_mem(addr);
return 0;
}
@ -330,8 +357,10 @@ x86_64_local_addr_space_init (void)
local_addr_space.acc.get_proc_name = get_static_proc_name;
unw_flush_cache (&local_addr_space, 0, 0);
#if NLGA > 0
memset (last_good_addr, 0, sizeof (unw_word_t) * NLGA);
lga_victim = 0;
#endif
}
#endif /* !UNW_REMOTE_ONLY */