Messages in this thread | | | Date | Sun, 27 Sep 2015 04:21:59 +0200 | From | angelo <> | Subject | Re: [PATCH] mm: fix cpu hangs on truncating last page of a 16t sparse file |
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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@sysam.it> >> --- >> 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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