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authorLinus Torvalds <torvalds@linux-foundation.org>2020-06-07 17:27:45 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-06-07 17:27:45 -0700
commitaf7b4801030c07637840191c69eb666917e4135d (patch)
treed4238c6c1fe6c06112f766ae5a90afde53644f78 /include/linux/u64_stats_sync.h
parentMerge git://git.kernel.org/pub/scm/linux/kernel/git/davem/sparc-next (diff)
parentnet: dsa: lantiq_gswip: fix and improve the unsupported interface error (diff)
downloadwireguard-linux-af7b4801030c07637840191c69eb666917e4135d.tar.xz
wireguard-linux-af7b4801030c07637840191c69eb666917e4135d.zip
Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net
Pull networking fixes from David Miller: - Fix the build with certain Kconfig combinations for the Chelsio inline TLS device, from Rohit Maheshwar and Vinay Kumar Yadavi. - Fix leak in genetlink, from Cong Lang. - Fix out of bounds packet header accesses in seg6, from Ahmed Abdelsalam. - Two XDP fixes in the ENA driver, from Sameeh Jubran - Use rwsem in device rename instead of a seqcount because this code can sleep, from Ahmed S. Darwish. - Fix WoL regressions in r8169, from Heiner Kallweit. - Fix qed crashes in kdump mode, from Alok Prasad. - Fix the callbacks used for certain thermal zones in mlxsw, from Vadim Pasternak. * git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net: (35 commits) net: dsa: lantiq_gswip: fix and improve the unsupported interface error mlxsw: core: Use different get_trend() callbacks for different thermal zones net: dp83869: Reset return variable if PHY strap is read rhashtable: Drop raw RCU deref in nested_table_free cxgb4: Use kfree() instead kvfree() where appropriate net: qed: fixes crash while running driver in kdump kernel vsock/vmci: make vmci_vsock_transport_cb() static net: ethtool: Fix comment mentioning typo in IS_ENABLED() net: phy: mscc: fix Serdes configuration in vsc8584_config_init net: mscc: Fix OF_MDIO config check net: marvell: Fix OF_MDIO config check net: dp83867: Fix OF_MDIO config check net: dp83869: Fix OF_MDIO config check net: ethernet: mvneta: fix MVNETA_SKB_HEADROOM alignment ethtool: linkinfo: remove an unnecessary NULL check net/xdp: use shift instead of 64 bit division crypto/chtls:Fix compile error when CONFIG_IPV6 is disabled inet_connection_sock: clear inet_num out of destroy helper yam: fix possible memory leak in yam_init_driver lan743x: Use correct MAC_CR configuration for 1 GBit speed ...
Diffstat (limited to 'include/linux/u64_stats_sync.h')
-rw-r--r--include/linux/u64_stats_sync.h43
1 files changed, 23 insertions, 20 deletions
diff --git a/include/linux/u64_stats_sync.h b/include/linux/u64_stats_sync.h
index 9de5c10293f5..c6abb79501b3 100644
--- a/include/linux/u64_stats_sync.h
+++ b/include/linux/u64_stats_sync.h
@@ -3,33 +3,36 @@
#define _LINUX_U64_STATS_SYNC_H
/*
- * To properly implement 64bits network statistics on 32bit and 64bit hosts,
- * we provide a synchronization point, that is a noop on 64bit or UP kernels.
+ * Protect against 64-bit values tearing on 32-bit architectures. This is
+ * typically used for statistics read/update in different subsystems.
*
* Key points :
- * 1) Use a seqcount on SMP 32bits, with low overhead.
- * 2) Whole thing is a noop on 64bit arches or UP kernels.
- * 3) Write side must ensure mutual exclusion or one seqcount update could
+ *
+ * - Use a seqcount on 32-bit SMP, only disable preemption for 32-bit UP.
+ * - The whole thing is a no-op on 64-bit architectures.
+ *
+ * Usage constraints:
+ *
+ * 1) Write side must ensure mutual exclusion, or one seqcount update could
* be lost, thus blocking readers forever.
- * If this synchronization point is not a mutex, but a spinlock or
- * spinlock_bh() or disable_bh() :
- * 3.1) Write side should not sleep.
- * 3.2) Write side should not allow preemption.
- * 3.3) If applicable, interrupts should be disabled.
*
- * 4) If reader fetches several counters, there is no guarantee the whole values
- * are consistent (remember point 1) : this is a noop on 64bit arches anyway)
+ * 2) Write side must disable preemption, or a seqcount reader can preempt the
+ * writer and also spin forever.
+ *
+ * 3) Write side must use the _irqsave() variant if other writers, or a reader,
+ * can be invoked from an IRQ context.
*
- * 5) readers are allowed to sleep or be preempted/interrupted : They perform
- * pure reads. But if they have to fetch many values, it's better to not allow
- * preemptions/interruptions to avoid many retries.
+ * 4) If reader fetches several counters, there is no guarantee the whole values
+ * are consistent w.r.t. each other (remember point #2: seqcounts are not
+ * used for 64bit architectures).
*
- * 6) If counter might be written by an interrupt, readers should block interrupts.
- * (On UP, there is no seqcount_t protection, a reader allowing interrupts could
- * read partial values)
+ * 5) Readers are allowed to sleep or be preempted/interrupted: they perform
+ * pure reads.
*
- * 7) For irq and softirq uses, readers can use u64_stats_fetch_begin_irq() and
- * u64_stats_fetch_retry_irq() helpers
+ * 6) Readers must use both u64_stats_fetch_{begin,retry}_irq() if the stats
+ * might be updated from a hardirq or softirq context (remember point #1:
+ * seqcounts are not used for UP kernels). 32-bit UP stat readers could read
+ * corrupted 64-bit values otherwise.
*
* Usage :
*