On Thu, Nov 05, 2015 at 10:23:15AM +1100, Gavin Shan wrote: >On Wed, Nov 04, 2015 at 10:07:50AM -0600, Rob Herring wrote: >>On Wed, Nov 4, 2015 at 7:12 AM, Gavin Shan <gwshan@xxxxxxxxxxxxxxxxxx> wrote: >>> In current implementation, unflatten_dt_node() is called recursively >>> to unflatten device nodes in FDT blob. It's stress to limited stack >>> capacity. >> >>Did you actually hit a problem? >> >>Now we have a max depth of 64. Seems like that should be plenty... Any >>idea how this compares to when we run out of stack space? >> > >When I rebased last revision (v6), particular below patch, to 4.3.rc6, >the kernel won't boot in P7 and P8 boxes. On P7 boxes, the stack overruns >according to the printed kernel messages. On P8 boxes, the /bin/init in >initramfs image can't be loaded/executed properly and it's potentially >caused by memory corruption. That's why I reworked it to avoid recursive >calling to unflatten_dt_node(). > Missed the link to the patch here: https://patchwork.ozlabs.org/patch/504512/ >The max depth "64" wasn't selected based on the stack usage. I was thinking >the device tree is converted to friendly *.dts format and it's using TAB >as the prefix for each line. If the device tree has 64 depth, Each line >in *.dts for leaf nodes have to be wrapped and spanning multiple lines. >That's why I choosed 64, maybe 32 is enough. Did you see a device-tree >that has more than 16 depth in field? :-) > >>> This avoids calling the function recursively, meaning the device >>> nodes are unflattened in one call on unflatten_dt_node(): two arrays >>> are introduced to track the parent path size and the device node of >>> current level of depth, which will be used by the device node on next >>> level of depth to be unflattened. Also, the parameter "poffset" and >>> "fpsize" are unused and dropped. >> >>Yay. I'm happy to see parameters removed instead of added to this function. >> >>> >>> Signed-off-by: Gavin Shan <gwshan@xxxxxxxxxxxxxxxxxx> >>> --- >>> drivers/of/fdt.c | 94 +++++++++++++++++++++++++++++++++----------------------- >>> 1 file changed, 56 insertions(+), 38 deletions(-) >>> >>> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c >>> index 173b036..f4793d0 100644 >>> --- a/drivers/of/fdt.c >>> +++ b/drivers/of/fdt.c >>> @@ -355,61 +355,82 @@ static unsigned long populate_node(const void *blob, >>> return fpsize; >>> } >>> >>> +static void reverse_nodes(struct device_node *parent) >>> +{ >>> + struct device_node *child, *next; >>> + >>> + /* In-depth first */ >>> + child = parent->child; >>> + while (child) { >>> + reverse_nodes(child); >>> + >>> + child = child->sibling; >>> + } >>> + >>> + /* Reverse the nodes in the child list */ >>> + child = parent->child; >>> + parent->child = NULL; >>> + while (child) { >>> + next = child->sibling; >>> + >>> + child->sibling = parent->child; >>> + parent->child = child; >>> + child = next; >>> + } >>> +} >>> + >>> /** >>> * unflatten_dt_node - Alloc and populate a device_node from the flat tree >>> * @blob: The parent device tree blob >>> * @mem: Memory chunk to use for allocating device nodes and properties >>> - * @poffset: pointer to node in flat tree >>> * @dad: Parent struct device_node >>> * @nodepp: The device_node tree created by the call >>> - * @fpsize: Size of the node path up at the current depth. >>> * @dryrun: If true, do not allocate device nodes but still calculate needed >>> * memory size >>> */ >>> static void *unflatten_dt_node(const void *blob, >>> void *mem, >>> - int *poffset, >>> struct device_node *dad, >>> struct device_node **nodepp, >>> - unsigned long fpsize, >>> bool dryrun) >> >>We can probably further simplify things by returning an int with >>negative being errors and positive being the size. Also, dryrun can be >>dropped and implied by mem and/or nodepp being NULL. >> > >Yeah, I think it's reasonable to return "size" from this function. "dryrun" >can be dropped and implied by NULL @mem. @nodepp can't be NULL. I perhaps >have separate patch to address it in next revision. > >>> { >>> - struct device_node *np; >>> - static int depth; >>> - int old_depth; >>> - >>> - fpsize = populate_node(blob, *poffset, &mem, dad, fpsize, &np, dryrun); >>> - if (!fpsize) >>> - return mem; >>> + struct device_node *root; >>> + int offset = 0, depth = 0; >>> + unsigned long fpsizes[64]; >>> + struct device_node *nps[64]; >> >>Use a define here. >> > >Fair enough, will do in next revision. I'm not good at naming. Would >"FDT_MAX_DEPTH" is a good one? > >>> >>> - old_depth = depth; >>> - *poffset = fdt_next_node(blob, *poffset, &depth); >>> - if (depth < 0) >>> - depth = 0; >>> - while (*poffset > 0 && depth > old_depth) >>> - mem = unflatten_dt_node(blob, mem, poffset, np, NULL, >>> - fpsize, dryrun); >>> + if (nodepp) >>> + *nodepp = NULL; >>> + >>> + root = dad; >>> + fpsizes[depth] = dad ? strlen(of_node_full_name(dad)) : 0; >>> + nps[depth++] = dad; >>> + while (offset >= 0 && depth < 64) { >>> + fpsizes[depth] = populate_node(blob, offset, &mem, >>> + nps[depth - 1], >>> + fpsizes[depth - 1], >>> + &nps[depth], dryrun); >>> + if (!fpsizes[depth]) >>> + return mem; >>> + >>> + if (!dryrun && nodepp && !*nodepp) >>> + *nodepp = nps[depth]; >>> + if (!dryrun && !root) >>> + root = nps[depth]; >>> + >>> + offset = fdt_next_node(blob, offset, &depth); >>> + } >>> >>> - if (*poffset < 0 && *poffset != -FDT_ERR_NOTFOUND) >>> - pr_err("unflatten: error %d processing FDT\n", *poffset); >>> + if (offset < 0 && offset != -FDT_ERR_NOTFOUND) >>> + pr_err("%s: Error %d processing FDT\n", >>> + __func__, offset); >> >>What about depth == 64 case? I think the behavior should be a WARN and >>ignore those nodes so we at least can continue to boot and see the >>error. Of course, if there is a phandle pointing to ignored nodes, we >>have to handle that too. >> > >Yeah, I'll have a WARN_ON(depth >= 64) in next revision. Sorry, I didn't >get the 2nd part of your comments: When depth > 64, the system won't work. >It might boot up. Why the phandle pointing to the ignored node has to be >dropped? > >>> >>> /* >>> * Reverse the child list. Some drivers assumes node order matches .dts >>> * node order >>> */ >>> - if (!dryrun && np->child) { >>> - struct device_node *child = np->child; >>> - np->child = NULL; >>> - while (child) { >>> - struct device_node *next = child->sibling; >>> - child->sibling = np->child; >>> - np->child = child; >>> - child = next; >>> - } >>> - } >>> - >>> - if (nodepp) >>> - *nodepp = np; >>> + if (!dryrun) >>> + reverse_nodes(root); >>> >>> return mem; >>> } >>> @@ -431,7 +452,6 @@ static void __unflatten_device_tree(const void *blob, >>> void * (*dt_alloc)(u64 size, u64 align)) >>> { >>> unsigned long size; >>> - int start; >>> void *mem; >>> >>> pr_debug(" -> unflatten_device_tree()\n"); >>> @@ -452,8 +472,7 @@ static void __unflatten_device_tree(const void *blob, >>> } >>> >>> /* First pass, scan for size */ >>> - start = 0; >>> - size = (unsigned long)unflatten_dt_node(blob, NULL, &start, NULL, NULL, 0, true); >>> + size = (unsigned long)unflatten_dt_node(blob, NULL, NULL, NULL, true); >>> size = ALIGN(size, 4); >>> >>> pr_debug(" size is %lx, allocating...\n", size); >>> @@ -467,8 +486,7 @@ static void __unflatten_device_tree(const void *blob, >>> pr_debug(" unflattening %p...\n", mem); >>> >>> /* Second pass, do actual unflattening */ >>> - start = 0; >>> - unflatten_dt_node(blob, mem, &start, NULL, mynodes, 0, false); >>> + unflatten_dt_node(blob, mem, NULL, mynodes, false); >>> if (be32_to_cpup(mem + size) != 0xdeadbeef) >>> pr_warning("End of tree marker overwritten: %08x\n", >>> be32_to_cpup(mem + size)); > >Thanks, >Gavin -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
