On Thu, 12 May 2011, [email protected] wrote: > > The patch below does not apply to the .38-stable tree. > If someone wants it applied there, or to any other stable or longterm > tree, then please email the backport, including the original git commit > id to <[email protected]>.
Thank you for reporting that the original of this patch failed to apply to the .33-longterm tree. Please apply instead the backport below. Thanks, Hugh commit 59a16ead572330deb38e5848151d30ed1af754bc backported Author: Hugh Dickins <[email protected]> Date: Wed May 11 15:13:38 2011 -0700 Subject: [PATCH] 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 <[email protected]> Cc: Konstantin Khlebnikov <[email protected]> Cc: <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1396,18 +1396,13 @@ repeat: if (sbinfo->free_blocks == 0 || shmem_acct_block(info->flags)) { spin_unlock(&sbinfo->stat_lock); - spin_unlock(&info->lock); - error = -ENOSPC; - goto failed; + goto nospace; } sbinfo->free_blocks--; inode->i_blocks += BLOCKS_PER_PAGE; spin_unlock(&sbinfo->stat_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; @@ -1476,6 +1471,24 @@ done: *pagep = filepage; return 0; +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); _______________________________________________ stable mailing list [email protected] http://linux.kernel.org/mailman/listinfo/stable
