On Wed, Jul 14, 2021 at 11:26:20AM +0530, Sumit Garg wrote:
> Currently the only user for debug heap is kdbnearsym() which can be
> modified to rather use statically allocated buffer for symbol name as
> per it's current usage. So do that and hence remove custom debug heap
> allocator.
>
> Note that this change puts a restriction on kdbnearsym() callers to
> carefully use shared namebuf such that a caller should consume the symbol
> returned immediately prior to another call to fetch a different symbol.
>
> Also, this change uses standard KSYM_NAME_LEN macro for namebuf
> allocation instead of local variable: knt1_size which should avoid any
> conflicts caused by changes to KSYM_NAME_LEN macro value.
>
> This change has been tested using kgdbtest on arm64 which doesn't show
> any regressions.
>
> Suggested-by: Daniel Thompson <daniel.thomp...@linaro.org>
> Signed-off-by: Sumit Garg <sumit.g...@linaro.org>
> Reviewed-by: Douglas Anderson <diand...@chromium.org>
Applied, thanks!
> ---
>
> Changes in v4:
> - Addressed minor comments from Doug.
> - Picked up Doug's review tag.
>
> Changes in v3:
> - Rebased to tip of upstream master.
> - Updated function header comment for kdbnearsym().
>
> Changes in v2:
> - Use single static buffer for symbol name in kdbnearsym() instead of
> per caller buffers allocated on stack.
>
> kernel/debug/kdb/kdb_debugger.c | 1 -
> kernel/debug/kdb/kdb_private.h | 5 -
> kernel/debug/kdb/kdb_support.c | 329 +++-----------------------------
> 3 files changed, 28 insertions(+), 307 deletions(-)
>
> diff --git a/kernel/debug/kdb/kdb_debugger.c b/kernel/debug/kdb/kdb_debugger.c
> index 0220afda3200..e91fc3e4edd5 100644
> --- a/kernel/debug/kdb/kdb_debugger.c
> +++ b/kernel/debug/kdb/kdb_debugger.c
> @@ -140,7 +140,6 @@ int kdb_stub(struct kgdb_state *ks)
> */
> kdb_common_deinit_state();
> KDB_STATE_CLEAR(PAGER);
> - kdbnearsym_cleanup();
> if (error == KDB_CMD_KGDB) {
> if (KDB_STATE(DOING_KGDB))
> KDB_STATE_CLEAR(DOING_KGDB);
> diff --git a/kernel/debug/kdb/kdb_private.h b/kernel/debug/kdb/kdb_private.h
> index 170c69aedebb..8dbc840113c9 100644
> --- a/kernel/debug/kdb/kdb_private.h
> +++ b/kernel/debug/kdb/kdb_private.h
> @@ -109,7 +109,6 @@ extern int kdbgetaddrarg(int, const char **, int*,
> unsigned long *,
> long *, char **);
> extern int kdbgetsymval(const char *, kdb_symtab_t *);
> extern int kdbnearsym(unsigned long, kdb_symtab_t *);
> -extern void kdbnearsym_cleanup(void);
> extern char *kdb_strdup(const char *str, gfp_t type);
> extern void kdb_symbol_print(unsigned long, const kdb_symtab_t *, unsigned
> int);
>
> @@ -233,10 +232,6 @@ extern struct task_struct *kdb_curr_task(int);
>
> #define GFP_KDB (in_dbg_master() ? GFP_ATOMIC : GFP_KERNEL)
>
> -extern void *debug_kmalloc(size_t size, gfp_t flags);
> -extern void debug_kfree(void *);
> -extern void debug_kusage(void);
> -
> extern struct task_struct *kdb_current_task;
> extern struct pt_regs *kdb_current_regs;
>
> diff --git a/kernel/debug/kdb/kdb_support.c b/kernel/debug/kdb/kdb_support.c
> index 9f50d22d68e6..c605b17b2a0d 100644
> --- a/kernel/debug/kdb/kdb_support.c
> +++ b/kernel/debug/kdb/kdb_support.c
> @@ -52,48 +52,48 @@ int kdbgetsymval(const char *symname, kdb_symtab_t
> *symtab)
> }
> EXPORT_SYMBOL(kdbgetsymval);
>
> -static char *kdb_name_table[100]; /* arbitrary size */
> -
> -/*
> - * kdbnearsym - Return the name of the symbol with the nearest address
> - * less than 'addr'.
> +/**
> + * kdbnearsym() - Return the name of the symbol with the nearest address
> + * less than @addr.
> + * @addr: Address to check for near symbol
> + * @symtab: Structure to receive results
> *
> - * Parameters:
> - * addr Address to check for symbol near
> - * symtab Structure to receive results
> - * Returns:
> - * 0 No sections contain this address, symtab zero filled
> - * 1 Address mapped to module/symbol/section, data in symtab
> - * Remarks:
> - * 2.6 kallsyms has a "feature" where it unpacks the name into a
> - * string. If that string is reused before the caller expects it
> - * then the caller sees its string change without warning. To
> - * avoid cluttering up the main kdb code with lots of kdb_strdup,
> - * tests and kfree calls, kdbnearsym maintains an LRU list of the
> - * last few unique strings. The list is sized large enough to
> - * hold active strings, no kdb caller of kdbnearsym makes more
> - * than ~20 later calls before using a saved value.
> + * WARNING: This function may return a pointer to a single statically
> + * allocated buffer (namebuf). kdb's unusual calling context (single
> + * threaded, all other CPUs halted) provides us sufficient locking for
> + * this to be safe. The only constraint imposed by the static buffer is
> + * that the caller must consume any previous reply prior to another call
> + * to lookup a new symbol.
> + *
> + * Note that, strictly speaking, some architectures may re-enter the kdb
> + * trap if the system turns out to be very badly damaged and this breaks
> + * the single-threaded assumption above. In these circumstances successful
> + * continuation and exit from the inner trap is unlikely to work and any
> + * user attempting this receives a prominent warning before being allowed
> + * to progress. In these circumstances we remain memory safe because
> + * namebuf[KSYM_NAME_LEN-1] will never change from '\0' although we do
> + * tolerate the possibility of garbled symbol display from the outer kdb
> + * trap.
> + *
> + * Return:
> + * * 0 - No sections contain this address, symtab zero filled
> + * * 1 - Address mapped to module/symbol/section, data in symtab
> */
> int kdbnearsym(unsigned long addr, kdb_symtab_t *symtab)
> {
> int ret = 0;
> unsigned long symbolsize = 0;
> unsigned long offset = 0;
> -#define knt1_size 128 /* must be >= kallsyms table size */
> - char *knt1 = NULL;
> + static char namebuf[KSYM_NAME_LEN];
>
> kdb_dbg_printf(AR, "addr=0x%lx, symtab=%px\n", addr, symtab);
> memset(symtab, 0, sizeof(*symtab));
>
> if (addr < 4096)
> goto out;
> - knt1 = debug_kmalloc(knt1_size, GFP_ATOMIC);
> - if (!knt1) {
> - kdb_func_printf("addr=0x%lx cannot kmalloc knt1\n", addr);
> - goto out;
> - }
> +
> symtab->sym_name = kallsyms_lookup(addr, &symbolsize , &offset,
> - (char **)(&symtab->mod_name), knt1);
> + (char **)(&symtab->mod_name), namebuf);
> if (offset > 8*1024*1024) {
> symtab->sym_name = NULL;
> addr = offset = symbolsize = 0;
> @@ -102,63 +102,14 @@ int kdbnearsym(unsigned long addr, kdb_symtab_t *symtab)
> symtab->sym_end = symtab->sym_start + symbolsize;
> ret = symtab->sym_name != NULL && *(symtab->sym_name) != '\0';
>
> - if (ret) {
> - int i;
> - /* Another 2.6 kallsyms "feature". Sometimes the sym_name is
> - * set but the buffer passed into kallsyms_lookup is not used,
> - * so it contains garbage. The caller has to work out which
> - * buffer needs to be saved.
> - *
> - * What was Rusty smoking when he wrote that code?
> - */
> - if (symtab->sym_name != knt1) {
> - strncpy(knt1, symtab->sym_name, knt1_size);
> - knt1[knt1_size-1] = '\0';
> - }
> - for (i = 0; i < ARRAY_SIZE(kdb_name_table); ++i) {
> - if (kdb_name_table[i] &&
> - strcmp(kdb_name_table[i], knt1) == 0)
> - break;
> - }
> - if (i >= ARRAY_SIZE(kdb_name_table)) {
> - debug_kfree(kdb_name_table[0]);
> - memmove(kdb_name_table, kdb_name_table+1,
> - sizeof(kdb_name_table[0]) *
> - (ARRAY_SIZE(kdb_name_table)-1));
> - } else {
> - debug_kfree(knt1);
> - knt1 = kdb_name_table[i];
> - memmove(kdb_name_table+i, kdb_name_table+i+1,
> - sizeof(kdb_name_table[0]) *
> - (ARRAY_SIZE(kdb_name_table)-i-1));
> - }
> - i = ARRAY_SIZE(kdb_name_table) - 1;
> - kdb_name_table[i] = knt1;
> - symtab->sym_name = kdb_name_table[i];
> - knt1 = NULL;
> - }
> -
> if (symtab->mod_name == NULL)
> symtab->mod_name = "kernel";
> kdb_dbg_printf(AR, "returns %d symtab->sym_start=0x%lx,
> symtab->mod_name=%px, symtab->sym_name=%px (%s)\n",
> ret, symtab->sym_start, symtab->mod_name,
> symtab->sym_name, symtab->sym_name);
> -
> out:
> - debug_kfree(knt1);
> return ret;
> }
>
> -void kdbnearsym_cleanup(void)
> -{
> - int i;
> - for (i = 0; i < ARRAY_SIZE(kdb_name_table); ++i) {
> - if (kdb_name_table[i]) {
> - debug_kfree(kdb_name_table[i]);
> - kdb_name_table[i] = NULL;
> - }
> - }
> -}
> -
> static char ks_namebuf[KSYM_NAME_LEN+1], ks_namebuf_prev[KSYM_NAME_LEN+1];
>
> /*
> @@ -656,230 +607,6 @@ unsigned long kdb_task_state(const struct task_struct
> *p, unsigned long mask)
> return (mask & kdb_task_state_string(state)) != 0;
> }
>
> -/* Last ditch allocator for debugging, so we can still debug even when
> - * the GFP_ATOMIC pool has been exhausted. The algorithms are tuned
> - * for space usage, not for speed. One smallish memory pool, the free
> - * chain is always in ascending address order to allow coalescing,
> - * allocations are done in brute force best fit.
> - */
> -
> -struct debug_alloc_header {
> - u32 next; /* offset of next header from start of pool */
> - u32 size;
> - void *caller;
> -};
> -
> -/* The memory returned by this allocator must be aligned, which means
> - * so must the header size. Do not assume that sizeof(struct
> - * debug_alloc_header) is a multiple of the alignment, explicitly
> - * calculate the overhead of this header, including the alignment.
> - * The rest of this code must not use sizeof() on any header or
> - * pointer to a header.
> - */
> -#define dah_align 8
> -#define dah_overhead ALIGN(sizeof(struct debug_alloc_header), dah_align)
> -
> -static u64 debug_alloc_pool_aligned[256*1024/dah_align]; /* 256K pool */
> -static char *debug_alloc_pool = (char *)debug_alloc_pool_aligned;
> -static u32 dah_first, dah_first_call = 1, dah_used, dah_used_max;
> -
> -/* Locking is awkward. The debug code is called from all contexts,
> - * including non maskable interrupts. A normal spinlock is not safe
> - * in NMI context. Try to get the debug allocator lock, if it cannot
> - * be obtained after a second then give up. If the lock could not be
> - * previously obtained on this cpu then only try once.
> - *
> - * sparse has no annotation for "this function _sometimes_ acquires a
> - * lock", so fudge the acquire/release notation.
> - */
> -static DEFINE_SPINLOCK(dap_lock);
> -static int get_dap_lock(void)
> - __acquires(dap_lock)
> -{
> - static int dap_locked = -1;
> - int count;
> - if (dap_locked == smp_processor_id())
> - count = 1;
> - else
> - count = 1000;
> - while (1) {
> - if (spin_trylock(&dap_lock)) {
> - dap_locked = -1;
> - return 1;
> - }
> - if (!count--)
> - break;
> - udelay(1000);
> - }
> - dap_locked = smp_processor_id();
> - __acquire(dap_lock);
> - return 0;
> -}
> -
> -void *debug_kmalloc(size_t size, gfp_t flags)
> -{
> - unsigned int rem, h_offset;
> - struct debug_alloc_header *best, *bestprev, *prev, *h;
> - void *p = NULL;
> - if (!get_dap_lock()) {
> - __release(dap_lock); /* we never actually got it */
> - return NULL;
> - }
> - h = (struct debug_alloc_header *)(debug_alloc_pool + dah_first);
> - if (dah_first_call) {
> - h->size = sizeof(debug_alloc_pool_aligned) - dah_overhead;
> - dah_first_call = 0;
> - }
> - size = ALIGN(size, dah_align);
> - prev = best = bestprev = NULL;
> - while (1) {
> - if (h->size >= size && (!best || h->size < best->size)) {
> - best = h;
> - bestprev = prev;
> - if (h->size == size)
> - break;
> - }
> - if (!h->next)
> - break;
> - prev = h;
> - h = (struct debug_alloc_header *)(debug_alloc_pool + h->next);
> - }
> - if (!best)
> - goto out;
> - rem = best->size - size;
> - /* The pool must always contain at least one header */
> - if (best->next == 0 && bestprev == NULL && rem < dah_overhead)
> - goto out;
> - if (rem >= dah_overhead) {
> - best->size = size;
> - h_offset = ((char *)best - debug_alloc_pool) +
> - dah_overhead + best->size;
> - h = (struct debug_alloc_header *)(debug_alloc_pool + h_offset);
> - h->size = rem - dah_overhead;
> - h->next = best->next;
> - } else
> - h_offset = best->next;
> - best->caller = __builtin_return_address(0);
> - dah_used += best->size;
> - dah_used_max = max(dah_used, dah_used_max);
> - if (bestprev)
> - bestprev->next = h_offset;
> - else
> - dah_first = h_offset;
> - p = (char *)best + dah_overhead;
> - memset(p, POISON_INUSE, best->size - 1);
> - *((char *)p + best->size - 1) = POISON_END;
> -out:
> - spin_unlock(&dap_lock);
> - return p;
> -}
> -
> -void debug_kfree(void *p)
> -{
> - struct debug_alloc_header *h;
> - unsigned int h_offset;
> - if (!p)
> - return;
> - if ((char *)p < debug_alloc_pool ||
> - (char *)p >= debug_alloc_pool + sizeof(debug_alloc_pool_aligned)) {
> - kfree(p);
> - return;
> - }
> - if (!get_dap_lock()) {
> - __release(dap_lock); /* we never actually got it */
> - return; /* memory leak, cannot be helped */
> - }
> - h = (struct debug_alloc_header *)((char *)p - dah_overhead);
> - memset(p, POISON_FREE, h->size - 1);
> - *((char *)p + h->size - 1) = POISON_END;
> - h->caller = NULL;
> - dah_used -= h->size;
> - h_offset = (char *)h - debug_alloc_pool;
> - if (h_offset < dah_first) {
> - h->next = dah_first;
> - dah_first = h_offset;
> - } else {
> - struct debug_alloc_header *prev;
> - unsigned int prev_offset;
> - prev = (struct debug_alloc_header *)(debug_alloc_pool +
> - dah_first);
> - while (1) {
> - if (!prev->next || prev->next > h_offset)
> - break;
> - prev = (struct debug_alloc_header *)
> - (debug_alloc_pool + prev->next);
> - }
> - prev_offset = (char *)prev - debug_alloc_pool;
> - if (prev_offset + dah_overhead + prev->size == h_offset) {
> - prev->size += dah_overhead + h->size;
> - memset(h, POISON_FREE, dah_overhead - 1);
> - *((char *)h + dah_overhead - 1) = POISON_END;
> - h = prev;
> - h_offset = prev_offset;
> - } else {
> - h->next = prev->next;
> - prev->next = h_offset;
> - }
> - }
> - if (h_offset + dah_overhead + h->size == h->next) {
> - struct debug_alloc_header *next;
> - next = (struct debug_alloc_header *)
> - (debug_alloc_pool + h->next);
> - h->size += dah_overhead + next->size;
> - h->next = next->next;
> - memset(next, POISON_FREE, dah_overhead - 1);
> - *((char *)next + dah_overhead - 1) = POISON_END;
> - }
> - spin_unlock(&dap_lock);
> -}
> -
> -void debug_kusage(void)
> -{
> - struct debug_alloc_header *h_free, *h_used;
> -#ifdef CONFIG_IA64
> - /* FIXME: using dah for ia64 unwind always results in a memory leak.
> - * Fix that memory leak first, then set debug_kusage_one_time = 1 for
> - * all architectures.
> - */
> - static int debug_kusage_one_time;
> -#else
> - static int debug_kusage_one_time = 1;
> -#endif
> - if (!get_dap_lock()) {
> - __release(dap_lock); /* we never actually got it */
> - return;
> - }
> - h_free = (struct debug_alloc_header *)(debug_alloc_pool + dah_first);
> - if (dah_first == 0 &&
> - (h_free->size == sizeof(debug_alloc_pool_aligned) - dah_overhead ||
> - dah_first_call))
> - goto out;
> - if (!debug_kusage_one_time)
> - goto out;
> - debug_kusage_one_time = 0;
> - kdb_func_printf("debug_kmalloc memory leak dah_first %d\n", dah_first);
> - if (dah_first) {
> - h_used = (struct debug_alloc_header *)debug_alloc_pool;
> - kdb_func_printf("h_used %px size %d\n", h_used, h_used->size);
> - }
> - do {
> - h_used = (struct debug_alloc_header *)
> - ((char *)h_free + dah_overhead + h_free->size);
> - kdb_func_printf("h_used %px size %d caller %px\n",
> - h_used, h_used->size, h_used->caller);
> - h_free = (struct debug_alloc_header *)
> - (debug_alloc_pool + h_free->next);
> - } while (h_free->next);
> - h_used = (struct debug_alloc_header *)
> - ((char *)h_free + dah_overhead + h_free->size);
> - if ((char *)h_used - debug_alloc_pool !=
> - sizeof(debug_alloc_pool_aligned))
> - kdb_func_printf("h_used %px size %d caller %px\n",
> - h_used, h_used->size, h_used->caller);
> -out:
> - spin_unlock(&dap_lock);
> -}
> -
> /* Maintain a small stack of kdb_flags to allow recursion without disturbing
> * the global kdb state.
> */
> --
> 2.25.1
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