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author | Hugh Dickins <hughd@google.com> | 2011-05-11 15:13:38 -0700 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2011-05-11 18:50:45 -0700 |
commit | 59a16ead572330deb38e5848151d30ed1af754bc (patch) | |
tree | 792b1f35e11e0f49170b0d306d45706de54afeae /mm/shmem.c | |
parent | 778dd893ae785c5fd505dac30b5fc40aae188bf1 (diff) | |
download | linux-stable-59a16ead572330deb38e5848151d30ed1af754bc.tar.gz linux-stable-59a16ead572330deb38e5848151d30ed1af754bc.tar.bz2 linux-stable-59a16ead572330deb38e5848151d30ed1af754bc.zip |
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>
Diffstat (limited to 'mm/shmem.c')
-rw-r--r-- | mm/shmem.c | 32 |
1 files changed, 22 insertions, 10 deletions
diff --git a/mm/shmem.c b/mm/shmem.c index dc17551d060a..9e755c166cc5 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1407,20 +1407,14 @@ repeat: if (sbinfo->max_blocks) { if (percpu_counter_compare(&sbinfo->used_blocks, sbinfo->max_blocks) >= 0 || - shmem_acct_block(info->flags)) { - spin_unlock(&info->lock); - error = -ENOSPC; - goto failed; - } + shmem_acct_block(info->flags)) + goto nospace; percpu_counter_inc(&sbinfo->used_blocks); spin_lock(&inode->i_lock); inode->i_blocks += BLOCKS_PER_PAGE; spin_unlock(&inode->i_lock); - } else if (shmem_acct_block(info->flags)) { - spin_unlock(&info->lock); - error = -ENOSPC; - goto failed; - } + } else if (shmem_acct_block(info->flags)) + goto nospace; if (!filepage) { int ret; @@ -1500,6 +1494,24 @@ done: error = 0; goto out; +nospace: + /* + * Perhaps the page was brought in from swap between find_lock_page + * and taking info->lock? We allow for that at add_to_page_cache_lru, + * but must also avoid reporting a spurious ENOSPC while working on a + * full tmpfs. (When filepage has been passed in to shmem_getpage, it + * is already in page cache, which prevents this race from occurring.) + */ + if (!filepage) { + struct page *page = find_get_page(mapping, idx); + if (page) { + spin_unlock(&info->lock); + page_cache_release(page); + goto repeat; + } + } + spin_unlock(&info->lock); + error = -ENOSPC; failed: if (*pagep != filepage) { unlock_page(filepage); |