tmpfs: fix spurious ENOSPC when racing with unswap
Testing the shmem_swaplist replacements for igrab() revealed another bug: writes to /dev/loop0 on a tmpfs file which fills its filesystem were sometimes failing with "Buffer I/O error"s. These came from ENOSPC failures of shmem_getpage(), when racing with swapoff: the same could happen when racing with another shmem_getpage(), pulling the page in from swap in between our find_lock_page() and our taking the info->lock (though not in the single-threaded loop case). This is unacceptable, and surprising that I've not noticed it before: it dates back many years, but (presumably) was made a lot easier to reproduce in 2.6.36, which sited a page preallocation in the race window. Fix it by rechecking the page cache before settling on an ENOSPC error. Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Konstantin Khlebnikov <khlebnikov@openvz.org> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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1 changed files with 22 additions and 10 deletions
32
mm/shmem.c
32
mm/shmem.c
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@ -1407,20 +1407,14 @@ repeat:
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if (sbinfo->max_blocks) {
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if (percpu_counter_compare(&sbinfo->used_blocks,
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sbinfo->max_blocks) >= 0 ||
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shmem_acct_block(info->flags)) {
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spin_unlock(&info->lock);
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error = -ENOSPC;
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goto failed;
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}
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shmem_acct_block(info->flags))
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goto nospace;
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percpu_counter_inc(&sbinfo->used_blocks);
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spin_lock(&inode->i_lock);
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inode->i_blocks += BLOCKS_PER_PAGE;
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spin_unlock(&inode->i_lock);
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} else if (shmem_acct_block(info->flags)) {
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spin_unlock(&info->lock);
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error = -ENOSPC;
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goto failed;
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}
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} else if (shmem_acct_block(info->flags))
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goto nospace;
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if (!filepage) {
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int ret;
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@ -1500,6 +1494,24 @@ done:
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error = 0;
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goto out;
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nospace:
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/*
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* Perhaps the page was brought in from swap between find_lock_page
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* and taking info->lock? We allow for that at add_to_page_cache_lru,
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* but must also avoid reporting a spurious ENOSPC while working on a
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* full tmpfs. (When filepage has been passed in to shmem_getpage, it
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* is already in page cache, which prevents this race from occurring.)
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*/
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if (!filepage) {
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struct page *page = find_get_page(mapping, idx);
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if (page) {
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spin_unlock(&info->lock);
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page_cache_release(page);
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goto repeat;
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}
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}
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spin_unlock(&info->lock);
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error = -ENOSPC;
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failed:
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if (*pagep != filepage) {
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unlock_page(filepage);
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