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exec.c: Fix breakpoint invalidation race

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A bug (1647683) was reported showing a crash when removing
breakpoints. The reproducer was bisected to 3359baad when tb_flush
was finally made thread safe. While in MTTCG the locking in
breakpoint_invalidate would have prevented any problems, but
currently tb_lock() is a NOP for system emulation.

The race is between a tb_flush from the gdbstub and the
tb_invalidate_phys_addr() in breakpoint_invalidate().

Ideally we'd have actual locking here; for the moment the
simple fix is to do a full tb_flush() for a bp invalidate,
since that is thread-safe even if no lock is taken.

Backports commit a9353fe897ca2687e5b3385ed39e3db3927a90e0 from qemu
This commit is contained in:
Peter Maydell 2018-03-01 09:10:52 -05:00 committed by Lioncash
parent f4c65739f3
commit 488b6cc82b
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GPG key ID: 4E3C3CC1031BA9C7
1 changed files with 6 additions and 20 deletions
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26
qemu/exec.c
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@ -522,29 +522,15 @@ void cpu_exec_init(CPUState *cpu, void *opaque)
#endif
}
#if defined(CONFIG_USER_ONLY)
static void breakpoint_invalidate(CPUState *cpu, target_ulong pc)
{
// Unicorn: commented out
mmap_lock();
//tb_lock();
tb_invalidate_phys_page_range(pc, pc + 1, 0);
//tb_unlock();
mmap_unlock();
/* Flush the whole TB as this will not have race conditions
* even if we don't have proper locking yet.
* Ideally we would just invalidate the TBs for the
* specified PC.
*/
tb_flush(cpu);
}
#else
static void breakpoint_invalidate(CPUState *cpu, target_ulong pc)
{
MemTxAttrs attrs;
hwaddr phys = cpu_get_phys_page_attrs_debug(cpu, pc, &attrs);
int asidx = cpu_asidx_from_attrs(cpu, attrs);
if (phys != -1) {
/* Locks grabbed by tb_invalidate_phys_addr */
tb_invalidate_phys_addr(cpu->cpu_ases[asidx].as,
phys | (pc & ~TARGET_PAGE_MASK));
}
}
#endif
#if defined(CONFIG_USER_ONLY)
void cpu_watchpoint_remove_all(CPUState *cpu, int mask)