Hi Hugh, thanks for the fast reply.. Looks like the XFS file system can support files until 16 Tera when CONFIG_LBDAF is enabled. On XFS, 32 bit arch, s_maxbytes is actually set (CONFIG_LBDAF=y) as 17592186044415. But if s_maxbytes doesn't have to be greater than MAX_LFS_FILESIZE, i agree the issue should be fixed in layers above. The fact is that everything still works correct until an index as 17592186044415 - 4096, and there can be users that could already have so big files in use in their setup. What do you think ? Best regards Angelo Dureghello On 27/09/2015 03:36, Hugh Dickins wrote:
Let's Cc linux-fsdevel, who will be more knowledgable. On Sun, 27 Sep 2015, angelo wrote:Hi all, running xfstests, generic 308 on whatever 32bit arch is possible to observe cpu to hang near 100% on unlink. The test removes a sparse file of length 16tera where only the last 4096 bytes block is mapped. At line 265 of truncate.c there is a if (index >= end) break; But if index is, as in this case, a 4294967295, it match -1 used as eof. Hence the cpu loops 100% just after.That's odd. I've not checked your patch, because I think the problem would go beyond truncate, and the root cause lie elsewhere. My understanding is that the 32-bit #define MAX_LFS_FILESIZE (((loff_t)PAGE_CACHE_SIZE << (BITS_PER_LONG-1))-1) makes a page->index of -1 (or any "negative") impossible to reach. I don't know offhand the rules for mounting a filesystem populated with a 64-bit kernel on a 32-bit kernel, what's to happen when a too-large file is encountered; but assume that's not the case here - you're just running xfstests/tests/generic/308. Is pwrite missing a check for offset beyond s_maxbytes? Or is this filesystem-dependent? Which filesystem? Hugh------------------- On 32bit archs, with CONFIG_LBDAF=y, if truncating last page of a 16tera file, "index" variable is set to 4294967295, and hence matches with -1 used as EOF value. This result in an inifite loop when unlink is executed on this file. Signed-off-by: Angelo Dureghello <angelo@xxxxxxxx> --- mm/truncate.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/mm/truncate.c b/mm/truncate.c index 76e35ad..3751034 100644 --- a/mm/truncate.c +++ b/mm/truncate.c @@ -283,14 +283,15 @@ void truncate_inode_pages_range(struct address_space *mapping, pagevec_remove_exceptionals(&pvec); pagevec_release(&pvec); cond_resched(); - index++; + if (index < end) + index++; } if (partial_start) { struct page *page = find_lock_page(mapping, start - 1); if (page) { unsigned int top = PAGE_CACHE_SIZE; - if (start > end) { + if (start > end && end != -1) { /* Truncation within a single page */ top = partial_end; partial_end = 0; @@ -322,7 +323,7 @@ void truncate_inode_pages_range(struct address_space *mapping, * If the truncation happened within a single page no pages * will be released, just zeroed, so we can bail out now. */ - if (start >= end) + if (start >= end && end != -1) return; index = start; @@ -337,7 +338,7 @@ void truncate_inode_pages_range(struct address_space *mapping, index = start; continue; } - if (index == start && indices[0] >= end) { + if (index == start && (indices[0] >= end && end != -1)) { /* All gone out of hole to be punched, we're done */ pagevec_remove_exceptionals(&pvec); pagevec_release(&pvec); @@ -348,7 +349,7 @@ void truncate_inode_pages_range(struct address_space *mapping, /* We rely upon deletion not changing page->index */ index = indices[i]; - if (index >= end) { + if (index >= end && (end != -1)) { /* Restart punch to make sure all gone */ index = start - 1; break; -- 2.5.3
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