From: Sunil Mushran Date: Thu, 21 Jan 2010 18:50:03 +0000 (-0800) Subject: ocfs2: Prevent a livelock in dlmglue X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=a19128260107f951d1b4c421cf98b92f8092b069;p=openwrt%2Fstaging%2Fblogic.git ocfs2: Prevent a livelock in dlmglue There is possibility of a livelock in __ocfs2_cluster_lock(). If a node were to get an ast for an upconvert request, followed immediately by a bast, there is a small window where the fs may downconvert the lock before the process requesting the upconvert is able to take the lock. This patch adds a new flag to indicate that the upconvert is still in progress and that the dc thread should not downconvert it right now. Wengang Wang and Joel Becker contributed heavily to this patch. Reported-by: David Teigland Signed-off-by: Sunil Mushran Signed-off-by: Joel Becker --- diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c index 0cdf63042b76..85d7c490755b 100644 --- a/fs/ocfs2/dlmglue.c +++ b/fs/ocfs2/dlmglue.c @@ -875,6 +875,14 @@ static inline void ocfs2_generic_handle_convert_action(struct ocfs2_lock_res *lo lockres_or_flags(lockres, OCFS2_LOCK_NEEDS_REFRESH); lockres->l_level = lockres->l_requested; + + /* + * We set the OCFS2_LOCK_UPCONVERT_FINISHING flag before clearing + * the OCFS2_LOCK_BUSY flag to prevent the dc thread from + * downconverting the lock before the upconvert has fully completed. + */ + lockres_or_flags(lockres, OCFS2_LOCK_UPCONVERT_FINISHING); + lockres_clear_flags(lockres, OCFS2_LOCK_BUSY); mlog_exit_void(); @@ -1134,6 +1142,7 @@ static inline void ocfs2_recover_from_dlm_error(struct ocfs2_lock_res *lockres, mlog_entry_void(); spin_lock_irqsave(&lockres->l_lock, flags); lockres_clear_flags(lockres, OCFS2_LOCK_BUSY); + lockres_clear_flags(lockres, OCFS2_LOCK_UPCONVERT_FINISHING); if (convert) lockres->l_action = OCFS2_AST_INVALID; else @@ -1324,13 +1333,13 @@ static int __ocfs2_cluster_lock(struct ocfs2_super *osb, again: wait = 0; + spin_lock_irqsave(&lockres->l_lock, flags); + if (catch_signals && signal_pending(current)) { ret = -ERESTARTSYS; - goto out; + goto unlock; } - spin_lock_irqsave(&lockres->l_lock, flags); - mlog_bug_on_msg(lockres->l_flags & OCFS2_LOCK_FREEING, "Cluster lock called on freeing lockres %s! flags " "0x%lx\n", lockres->l_name, lockres->l_flags); @@ -1347,6 +1356,25 @@ again: goto unlock; } + if (lockres->l_flags & OCFS2_LOCK_UPCONVERT_FINISHING) { + /* + * We've upconverted. If the lock now has a level we can + * work with, we take it. If, however, the lock is not at the + * required level, we go thru the full cycle. One way this could + * happen is if a process requesting an upconvert to PR is + * closely followed by another requesting upconvert to an EX. + * If the process requesting EX lands here, we want it to + * continue attempting to upconvert and let the process + * requesting PR take the lock. + * If multiple processes request upconvert to PR, the first one + * here will take the lock. The others will have to go thru the + * OCFS2_LOCK_BLOCKED check to ensure that there is no pending + * downconvert request. + */ + if (level <= lockres->l_level) + goto update_holders; + } + if (lockres->l_flags & OCFS2_LOCK_BLOCKED && !ocfs2_may_continue_on_blocked_lock(lockres, level)) { /* is the lock is currently blocked on behalf of @@ -1417,11 +1445,14 @@ again: goto again; } +update_holders: /* Ok, if we get here then we're good to go. */ ocfs2_inc_holders(lockres, level); ret = 0; unlock: + lockres_clear_flags(lockres, OCFS2_LOCK_UPCONVERT_FINISHING); + spin_unlock_irqrestore(&lockres->l_lock, flags); out: /* @@ -3402,6 +3433,18 @@ recheck: goto leave; } + /* + * This prevents livelocks. OCFS2_LOCK_UPCONVERT_FINISHING flag is + * set when the ast is received for an upconvert just before the + * OCFS2_LOCK_BUSY flag is cleared. Now if the fs received a bast + * on the heels of the ast, we want to delay the downconvert just + * enough to allow the up requestor to do its task. Because this + * lock is in the blocked queue, the lock will be downconverted + * as soon as the requestor is done with the lock. + */ + if (lockres->l_flags & OCFS2_LOCK_UPCONVERT_FINISHING) + goto leave_requeue; + /* if we're blocking an exclusive and we have *any* holders, * then requeue. */ if ((lockres->l_blocking == DLM_LOCK_EX) diff --git a/fs/ocfs2/ocfs2.h b/fs/ocfs2/ocfs2.h index 9362eea7424b..740f448041e2 100644 --- a/fs/ocfs2/ocfs2.h +++ b/fs/ocfs2/ocfs2.h @@ -136,6 +136,10 @@ enum ocfs2_unlock_action { #define OCFS2_LOCK_PENDING (0x00000400) /* This lockres is pending a call to dlm_lock. Only exists with BUSY set. */ +#define OCFS2_LOCK_UPCONVERT_FINISHING (0x00000800) /* blocks the dc thread + * from downconverting + * before the upconvert + * has completed */ struct ocfs2_lock_res_ops;